July 31 2005 – 02:00 UTC
The tropical wave passing over Hispaniola is still being monitored for signs of organization. Yesterday evening, the forecast took the bulk of low level energy north of Hispaniola. Over the past 24 hours, the low level circulation spotted yesterday has moved into the Dominican Republic, however. Interaction with land will inhibit tropical development another 24 hours. Notwithstanding, the northern end of the sharp wave axis is north of Puerto Rico. In addition to land interaction, the upper low to the northwest of the wave axis is still generating 30-40 knots of shear. All global model guidance dissipates this upper low within 24-48 hours. The available model guidance can be backed up by water vapor trends, which clearly show the upper low weakening ever so slightly. Upper level winds will begin to relax over the southwest Atlantic once this feature is no longer present. Otherwise, atmospheric conditions will remain hostile for tropical cyclogenesis for the next 24-48 hours. The SHIPS intensity model has strengthened 92L significantly for several runs and that has not changed. One should know that the system under investigation must be initalized in the model as a tropical depression in order for it to run properly. Therefore, the intensity forecasts should be taken with a grain of salt, but they should not be dismissed entirely. Development is no longer expected within the next 24-36 hours, but it is still considered quite possible beyond that period.
Global model tracks are in much better agreement than they were 24 hours ago. First, a few models do take some of the wave’s energy westward into the eastern Gulf of Mexico, and that does seem possible given the current low level steering flow and the way in which the wave is tangled up over Hispaniola at the moment. But all of the models take the bulk of wave energy east and north of Florida. The GFS model initially took a weak inverted wave towards southern Florida and the Florida Staights a few days ago. Yesterday, the model began to develop the northern end of the wave followed by taking it out to sea towards Bermuda. Today, the 18Z GFS run continues to show development of the northern end of the wave axis just east of the northern Bahamas. By Day 6, the model shows a broad surface low east-southeast of Cape Hatteras before it is pushed out to sea by an approaching upper trough. The NOGAPS model has been flip-flopping between Florida and the Carolina for several days. Yesterday, the model took a broad area of low pressure westward followed by recurvature along the west coast of the Florida Peninsula. Today’s 12Z run now shows the majority of low to mid level energy over the northern Bahamas by Day 4. By Day 6, the model indicates a closed surface circulation with 20-25 knot winds moving over Cape Hatteras. The 18Z run of the NOGAPS is not available. The ECMWF has also shifted. There was some question whether the model took the wave into the Gulf or up the East Coast the last couple days, but today it’s obvious. by Day 5, an 850MB low is centered over the northern Bahamas. By Day 6, a low is still over the Bahamas, but a northern piece of the wave splits and begins to develop near Bermuda. The Canadian model is the easternmost outlier. The CMC develops a tropical storm along the northern end of the wave and takes it just west of Bermuda before going out to sea. Meanwhile, the UKMET is still, by far, the most consistent model thus far. The 12Z run takes an 850MB vorticity into the northern Bahamas by Day 5 while hinting at surface low development. The track through Day 5 suggests a continued path toward the Carolinas. The Day 6 forecast was not available.
While 92L INVEST still looks like a mess, the potential for development in a few days should not be ignored. All global model guidance indicates that the main wave axis will be well to the north of Hispaniola in a couple days. Furthermore, the upper level low, which is responsible for the hostile upper wind regime, is forecast to weaken significantly or dissipate altogether within 48-72 hours. The two main factors that have been inhibiting development for the last several days should be nonexistant by 72 hours. Furthermore, global models continue to show potential surface reflection south of the Carolinas by Day 5. Other than the SHIPS intensity forecast, which should be taken with a grain of salt, there are no indications of an East Coast hurricane threat. However, it is very possible for Tropical Depression or Tropical Storm formation within 3-6 days. Even if a classified tropical cyclone does not form, the low pressure area could affect the weather along the East Coast, and regional National Weather Service offices will tweak their forecasts accordingly.
93L INVEST was left for dead once it collapsed in the eastern Atlantic, but it has since come to life. Convection has increased significantly over thre last 24 hours, and a mid level circulation is also visible on satellite imagery. Low level inflow is lacking, however. 93L is moving westward at a low latitude, and the upper low affecting 92L INVEST is not a factor in regards to this system. In fact, a deep layer ridge is aloft, and upper level winds are favorable for intensification. Nevertheless, there is a lot of dry air over the entire Caribbean Sea. No global models are developing 93L yet. Some slow development is possible over the next few days, and a TPC reconnaissance aircraft is scheduled to invesitgate this area tomorrow afternoon.
In the eastern Pacific, a broad low near 120ºW has a slight chance to develop within the next 36 hours before being sheared apart. This low will not affect any landmasses. Meanwhile, a much larger low pressure system near 10ºN/100ºW has some potential to develop within 3-5 days. This system is not expected to affect land either.
In the western Pacific, Tropical Storm Washi (08W) is forecast to hit northern Vietnam with 40-45 knot winds in 12-24 hours. Meanwhile, a Tropical Cyclone Formation Alert has been issued for the tropical disturbance just north of Yap. This disturbance has the potential to become a tropical storm or typhoon over the next few days. In the medium range, northeast China or Japan could be threatened. In addition, global models suggest the development of yet another tropical cyclone in the mid-latitudes near 25ºN/150ºE in 3-6 days. This progged tropical cylone will also have to be monitored as it could also pose a threat to Japan.
July 30 2005 – 02:00 UTC
92L INVEST, a tropical wave passing over the northeast Caribbean Sea, continues to show signs of gradual organization. One has to consider its progression over the last 48-72 hours. Over the last 6-12 hours, low level banding features have become better defined, low level inflow in the southern semicircle has been on the increase, and a low to mid level circulation has been spotted east-southeast of Puerto Rico on radar and satellite imagery. the only feature inhibiting development is the upper level low south-southwest of Bermuda. The upper low is generating 30-40 knot upper level winds over the northern half of 92L. While the 500MB low has been moving westward in tandem with the wave, global models suggest that the distance between the two features will increase over the next few days. Conditions are expected to be relatively favorable for intensification over the western Atlantic and the Bahamas. The SHIPS intensity model continues to develop 92L into a minimal hurricane within five days. This model will be increasingly reliable once 92L becomes a depression; the wave has already escaped the aforementioned Saharan Air Layer. The main energy associated with the wave is not expected to continue westward into mountainous Hispaniola. The 12Z UKMET and CMC continue to suggest that the developing surface low will move north of Hispaniola, and current satellite imagery shows the majority of convection and the potential low level energy lifting into the western Atlantic this evening.
The expected track of 92L is still relatively uncertain. The 18Z NOGAPS seems bogus as it takes the low level circulation westward through Hispaniola and eastern Cuba before it shows recurvature along the Florida peninsula. This scenario wouldn’t be so unlikely if the wave was weak and had no chance of development. The subtropical ridge does extend as far west as Florida in low level 700MB-850MB steering layer. The GFS has completely reversed its initial westerly track towards Florida and has since shifted closer to Bermuda as of 18Z. A track this far east seems unlikely as it appears to be downplaying the strength of the subtropical ridge in the low to mid levels; the model does not depict development. The Canadian model remains just east of the Carolinas while the UKMET outlines the potential threat to the Carolinas. The UKMET shows an 850MB vorticy passing east and north of Puerto Rico (slightly too far north in the short term) and entering the northern Bahamas by 72 hours. The model then projects a northerly track towards the Carolinas through 144 hours. The UKMET has been the most consistent model and it has been in the middle of the global model tracks thus far. Moreover, such a track seems fairly likely if the low were to deepen over the Bahamas as progged by the model. A significant weakness is still in place over the East Coast in the mid to upper levels. In conclusion, we still do not anticipate a track towards the Florida coast. The low is forecast to deepen into a Tropical Depression or Tropical Storm once over or near the southeast Bahamas followed by a turn towards the northwest within the next 72 hours. If this forecast were to verify, then 92L could pose a threat to the Carolinas. The only other scenario is more rapid recurvature as depicted by the CMC and GFS models, but that is not expected at this time. Again, the path of 92L is not certain and all interests in the Bahamas and southeast US from Florida northward to North Carolina are advised to monitor this system.
The remaining tropical waves east of the Lesser Antilles are showing no signs of development. Homegrown development near the coast of Florida or northwest Gulf of Mexico is not expected at this time.
July 29 2005 – 02:00 UTC
Tropical Storm Franklin continues to intensify. Satellite imagery indicates a much better convective symmetry and an improved outflow regime as it moves off to the northeast. This is occurring as a progressive trough begins to interact, helping to enhance a poleward outflow channel and thus amplifying the storm itself. Some additional increase in strength is lpossible over the next 12 hours, and Franklin could max out as high as 60KT before losing its tropical characteristics and merging with the trough.
The main focus today remains INVEST 92L, a tropical wave and associated 1013MB surface low near 17ºN/57ºW. This system has gradually become better organized today per satellite imagery; upper-level outflow is clear to the north and convection is more much consolidated near the center. Vast improvement is noted when compared to 36 hours ago, when it was barely more than a broad tropical wave with isolated convection and ingested dry air. The anticyclone aloft is centered a bit southwest of the center, so little outflow is noted on the southern quadrant. Several weak mid-level circulations are also detectable in satellite imagery, so in an absolute sense, organization is still somewhat lacking. Nonetheless, conditions are gradually becoming more conducive. The upper-level trough to the west is currently inducing moderate southwesterly shear upon the area. This feature will continue to be somewhat of a problem over the next day or so, but after that time is progged to slowly lift away. The Saharan Air Layer previously entrained in the circulation has decreased as well. Global model guidance suggests a favorable environment once in the Bahamas vicinity after Day 3 or so, after the trough makes way for conducive upper-level ridging. An aircraft reconaissance is scheduled to investigate 92L tomorrow, if necessary. Further development into Tropical Depression status is likely over the next 48 hours.
The future track of 92L is largely dependant on the strength and alignment of the subtropical ridge to the north. Over the next few days, the ridge should allow for a continued west-northwest motion, taking it just a hair north of the Leeward Islands and towards the Bahamas. Global model guidance is in strong agreement on this track, but there is a bit more divergence in the solutions the end of the forecast period. The NOGAPS model has been flip-flopping between a track towards Florida and the Carolinas. The 18Z run now depicts a weak surface low curving north near West Palm Beach, Florida, at Day 5 and hints of a Carolinas brush by Day 6. The GFS has also been very inconsistent. The last several runs have taken an inverted wave towards southern Florida. However, the 18Z run now splits the wave over the Bahamas; the northern half ejects northeast and out to sea while the southern half spreads west into Florida. The ECMWF, which has been the only model that clealry suggested a track towards the Gulf, is attempting to shift northward up the East Coast as of 12Z. Meanwhile, the UKMET and CMC have become bullish on tropical cyclogenesis just east of the Bahamas. Both models also suggest recurvature before the East Coast, and just east of the Outerbanks of North Carolina. The main assumption concerning the track is the idea of at least some development once north of Puerto Rico and east of the Bahamas. A more northerly track is favored due to the large weakness in the steering flow currently along the East Coast in the mid levels, and the lack of development shown by the GFS and NOGAPS models. All of the global models suggest that the subtropical ridge will temporarily strengthen just east of Florida, but a stronger tropical cyclone would have a slightly more poleward bias, and it would feel the effects of a mid level trough over the East Coast more than an inverted wave. If a notherly turn near the northern Bahamas does transpire, then the question will become whether the Carolinas will feel the directly effects of the tropical cyclone or if veers off to the northeast. Due to the Canadian model’s rightward bias all season and the inability of the UKMET to lock onto a medium range track, it is quite possible that the Carolinas, more so North Carolina, could be at risk. It should be noted that some of these medium range ideas are hardly more than conjectures. If 92L fails to close off a surface circulation over the next 48 hours, then the end result very well could be a southerly track towards Florida.
The remaining waves in the central and eastern Atlantic have become very disorganized over the last 12-24 hours. There is little to no chance of development in the short term.
July 28 2005 – 22:00 UTC
Tropical Storm Franklin has made a bit of a comeback today. Convection has flared a bit closer to the center and the cloud pattern has become slightly better organized. An additional 5-10KT increase in strength is very possible before the storm becomes carried northward by an upper trough. On this projected track, the storm should stay well offshore the US east coast.
A large-amplitude tropical wave, INVEST 92L, and associated broad 1013MB low is approaching 50ºW. The low is currently positioned on the southern end of the wave axis, however visible imagery depicts greater low-level curvature further north. Furthermore, dry Saharan Air is still wrapped within the wave, particularly on the northern side, which is keeping convective flare-ups to a minimum. Thus, the system still needs to consolidate more and enter a more unstable environment before development becomes an imminent concern. Having said this, conditions become increasingly more favorable closer to the Windward islands and all the way to the Bahamas. Oceanic heat content is high, coinciding with unseasonably warm sea-surface temperatures. Upper-level wind shear is on the low side, with the core westerly winds from the subtropical jet remaining well to the north. In fact, the latest CIMSS GOES-12 analysis indicates ridging is slowly increasing aloft the wave. Moreover, the influence of the Saharan Air Layer is lessening as it progresses further west. All of this data suggests that while the wave is far from being a classified tropical cyclone, further organization and increasing convection seems likely over the next few days. Given the extent of the environmental favorability where 92L is headed, a tropical depression cannot be ruled out within the next 48-60 hours.
INVEST 92L is moving generally west-northwestward. Global model guidance is rather converged on the projected track. The 12Z NOGAPS, UKMET, CMC, and ECMWF plus 18Z GFS all show a continued west-northwest motion through or just north of the Leeward Islands over the next 48 hours and then passing in the vicinity of the Bahamas by the end of the forecast period. Once near the Bahamas on Day Six, models vary on the precise alignment and strength of the ridge weakness over the eastern US and the ridge itself. The ECMWF, usually a reasonable medium-range model, takes the system all the way into the Gulf of Mexico by the middle of next week. Although it is somewhat of an outlier and no other model seems to show as intense of a ridge as the ECMWF depicts, it is worth noting the strong right bias in the model consensus for storms in this area during 2004 and early this season. The GFS slows it down in the Bahamas under supposedly collapsed steering currents, similar to what recently took place with Franklin the same area earlier last week, whereas the others show what seems to be a straight shot to somewhere along the southeast US coast beyond the runs’ time frames. Development from this area is not a certainty, though the chance is very much there. IF this does consolidate and become a tropical cyclone, conditions should favor quicker intensification once in the Bahamas and we could be faced with a hurricane threat. “If” is the key word.
Behind INVEST 92L, another tropical wave and mid-level center is noted, dubbed INVEST 93L. This system looked very well organized for a brief time late last night but has since become weaker. First off, the wave is not high-amplitude like the one discussed above, thus making it more susceptible to unfavorable conditions. Convection is sporadic in nature and there are no signs of either a surface low or a ridge aloft. Although sea surface temperatures are warm, this system is experiencing increased shear from the upper-level anticyclone to the west. As this ridge continues to build aloft 92L, this hinderance may only worsen with time. Furthermore, 93L is under moderate Saharan Air Layer influence from the north and east. Global models are not aggressive on developing the storm; none show anything more than a weak low in the shadows of a stronger system over the next six days. It is possible that some slow development could occur once and if the system can achieve a low-level circulation, though even so, anything significant seems unlikely. The future track is a moot point given the low prospects, but if a storm were to develop it would likely follow west-northwestward on the heels of the wave discussed above.
Yet another area of convection has emerged off the coast of Africa, behind both aformentioned INVESTs. This has not yet been identified in association with a tropical wave, but is rather a result of the intertropical convergence zone. Today’s runs of the GFS and NOGAPS indicate this will become a tropical cyclone in the forecast period as it too moves west-northwestward. No other model has yet shown any significant development, so there is not a convincing consensus at this time. One plus for this system is that it is at a relatively low latitude, which may prevent it from experiencing the core of the Saharan Air Layer. Since conditions are apparently not that unfavorable, this system will be monitored as it traverses the tropical Atlantic.
Some global models are hinting at increased low-level vorticity in the northern Gulf of Mexico on the tail end of a trough split in the next 4-5 days. None develop a true tropical cyclone, and any low that does form would probably have to work hard to make it to the surface, not to mention it would be a primarily baroclinic origination. This will too be watched, though nothing is expected at this time.
Two INVESTS in the West Pacific, one in the South China Sea and the other well east of the Philippines, have potential for further development over the next few days.
IWIC Worldwide Tropical Weather Discussion – July 27 2005 – 02:00 UTC
Tropical Storm Franklin just will not quit. Upper level westerly winds continue to expose the low level surface circulation, but convection always redevelops soon thereafter. Some fluctuations in intensity are possible over the next 24 hours before a second upper trough lifts Franklin northward and absorbs the TC. All model guidance takes the system north and away from Bermuda.
A high amplitude tropical wave and associated 1013MB low, now designated with the name 92L INVEST by the NAVY, is located near 10ºN/42ºW . There are a lot of factors that support intensification. 92L has a well defined signature, sea surface temperatures are warm, and upper level winds are light. A deep layer ridge in the mid and upper levels is present from the coast of Africa westward to 50ºW in the central Atlantic. This deep layer ridge will retrograde westward with 92L, much like the same setup with tropical wave’s Dennis and Emily. The 18Z run of the SHIPS intensity model brings 92L up to minimal hurricane strength by Day 5, which is when the system will be passing over the Lesser Antilles. However, none of the global models show significant tropical development over the next six days, and there is good reason for that. The Saharan Air Layer (SAL) is fully entrained into the weak surface low along the wave axis. The dry air entrainment is easily visible on eastern Atlantic water vapor imagery and CIMSS Meteosat-8 SAL imagery. Much of the atmosphere over the central Atlantic is fairly stable at the moment. Tropical cyclogenesis of 92L INVEST east of Puerto Rico is not anticipated. If the wave’s excellent signature persists as it approaches 20ºN and 65ºW-70ºW, then we may have to watch for development near the Bahamas. This forecast is still subject to change, and interests in the Lesser Antilles should continue to monitor the progress of 92L. Should the SAL weaken more than expected, then formation could occur much quicker than forecast.
Another vigorous tropical wave has exited the coast of Africa, and it has also been classified 93L INVEST by the NAVY. Conditions are much more favorable for tropical cyclogenesis of 93L than 92L. Sea surface temperatures are equally conducive, but 93L is directly centered underneath the deep layer ridge. Furthermore, 93L does not have to contend with the Saharan Air Layer nearly as much. The first high amplitude wave can be considered the frontrunner, and it is clearing out all the dry air ahead of 93L. Convection has been numerous, but another 12-24 hours of persistence over the eastern Atlantic is warranted. Slow development into a Tropical Depression is possible over the next 24-48 hours. It is too early to determine the threat it could pose to the Lesser Antilles. Some of the global models are indicating that the upper trough that will steer the remant of Franklin will weaken the subtropical ridge, which could steer 93L north of the islands. However, the data as of 12Z is considered inconclusive.
A third tropical wave has entered the eastern Atlantic within the last 6 hours. This wave will also be monitored for signs of development.
The global models are also developing a low pressure area well east of Bermuda in the medium range. This low could be hybrid or nontropical in nature, however. This progged low will be monitored.
Tropical Storm Banyan (07W) is dissipating east-northeast of Tokyo, Japan.
A large, disorganized area of thunderstorm activity located north of New Guinea will be watched closely for development in the western Pacific. The NOGAPS and GFS lift this area northward and hint at tropical cyclone formation in the medium range.
July 26 2005 – 01:00 UTC
Tropical Storm Franklin is highly disorganized. The low level circulation center has been exposed for at least 24-36 hours due to westerly shear. Upper level conditions are expected to remain unfavorable over the next several days, and Franklin should dissipate relatively soon. However, the the eastern semicircle of Franklin is the most intense, and even if the LLCC passes just north of Bermuda, the island will still face the brunt of the storm. Furthermore, the center may come closer to the island than the official forecast track is indicating. Tropical depression force winds with gusts to tropical storm intensity along with occasional squalls should be expected.
Tropical Storm Gert made landfall near Tampico, Mexico, overnight and is now dissipating. The last official advisory on Tropical Depression Gert was issued at 11AM EDT.
The central and eastern Pacifc remain very quiet. There is not one disturbance that shows any potential of tropical cyclone development, nor does any global model suggest an increasing probability of formation within the next 6-7 days.
There are several tropical waves in the eastern Atlantic and western Africa that will have to be monitored for tropical cyclone formation in the medium range. None of the global models except the GFS develop any of these waves into a significant TC, but that is not unusual. It is quite possible that the 8th system of the 2005 season could form within the next 10 days; not too many breaks this year. The Lesser Antilles should continue to monitor these waves.
Tropical Storm Banyan (07W) is making landfall over southern Japan. Maximum sustained winds are 45 knots, which should not cause significant structural wind damage. However, heavy rainfall and potential flooding could be a problem over the next 36 hours and beyond that period for central and northern Japan.
The remainder of the western Pacific is quiet. The GFS model wants to develop a tropical storm south-southwest of the Northern Marianas within 5-6 days but there is no other model support at this time.
July 22 2005 – 18:00 UTC
Tropical Storm Franklin is now moving northward away from the Bahamas. The storm is gradually becoming better organized. The outflow regime is much better defined, especially to the south and north of the center, and convective banding features have likewised improved. The upper environment surrounding Franklin is becoming more favorable, which is allowing the storm to gain organization as it has today. The anticyclone to the southwest has slid further left while Franklin has moved further north; this increased distance has ceased the restriction and shearing on the southwest side of the storm. In fact, several global models amplify an anticyclone on top of Franklin itself over the next day or so before becoming intertwined with the trough. Given this probability plus low shear and warm Gulf stream waters, further strengthening is likely. Franklin has a good chance of becoming a minimal hurricane sometime this weekend.
Our opinion on the storm’s future track has not changed much from yesterday. Franklin is currently along the left periphery of a ridge of high pressure, which is inducing straight southerly flow over the area. Strong westerlies are still streaming along 35ºN from the east coast to Bermuda’s vicinity. This pattern, very clearly seen on the latest CIMSS 700-850MB steering level map, is not progged to change much over the next 72 hours. Therefore, Franklin will be guided further north over the next day or so followed by a curve to the east-northeast. Global models are in tight agreement on this general track, all of them keeping the storm well offshore the southeast US coast. The only models that still take the storm into Florida or linger it in its current spot are the tropical models. However, these models have very poor performance for tropical cyclones interacting with and near baroclinic features, which applies to nearly every storm above 20ºN. Therefore, they are given little to no weight for this storm, and the fact that they are an outlier to every single reliable global model makes them seem even more skewed. The only way Franklin will curve back to the west is if it fully misses the connection with the trough. Since this is not offered in any of the models at this time, and based on the steering layers the storm will become too involved in the trough soon, such a scenario remains by far the least likely. Franklin is forecast to move towards sea or perhaps Bermuda as a minimal hurricane.
Other than Franklin, another tropical wave is generating strong masses of convection over the Yucatan Peninsula and adjacent waters. Visible satellite imagery depicts a possible low-level circulation developing just offshore the southern coastline of the eastern Yucatan. The strong anticyclonic flow noted yesterday has weakened, though this should regain defination once the system emerges into the southwest Gulf of Mexico. When this commences, conditions will be favorable for development. The shearing environment is expected to be low, especially with the anticyclone over the system which will act as a shield to any countering winds. Global models as a whole only show marginal development, no more than a weak tropical storm at face value. However keep in mind these models barely picked up on the systems that became Bret and Cindy a few weeks ago. The fact that there’s 1)already an incipient disturbance in place, 2)moving into a favorable upper environment, and 3)models pick up on increased low-level vorticity, tropical cyclone development is a distinct possibility. Models currently take whatever shows up on the runs into northeastern Mexico or southern Texas by Day 4. There has been a slight trend to the east since yesterday, though it is this general area that has the best chance of landfall. The limit on intensification will be the lack of time over water, and thus if a tropical cyclone does develop as is expected, it would probably be no more than a tropical storm.
In the deep tropical Atlantic, several waves are traversing the region. However, conditions are not perfectly favorable for development, and none are showing any strong signs of organization at this time.
In the West Pacific, Tropical Storm Nalgae is weakening well east of Japan. Tropical Storm Banyan, on the other hand, is intensifying and expected to become a typhoon over the next 48-72 hours. This system bears watching in Japan, as several models take it there before the forecast period is over.
July 21 2005 – 21:00 UTC
A tropical low located just east of the Bahamas has shown increasing signs of organization and persistence over the last 24 hours. Visible floater imagery outlines a decent low to mid level circulation representation. TPC Aircraft Reconnaissance is flying into the disturbance to determine if a surface circulation has formed. If Recon does find a closed circulation, then advisories on Tropical Depression 6 or possibly even Tropical Storm Franklin could be initiated at 5PM EDT depending on the maximum sustained winds found. Even if Recon does not find a closed off circulation, tropical development is likely within the next 24 hours. The upper air environment is becoming increasingly favorable for tropical cyclogenesis. An upper level ridge is developing over the Delmarva Peninsula, which will protect the developing surface low from an upper trough near 30ºN/60ºW increasing westerly winds. Furthermore, the aforementioned trough is being allowed to sink further south near 65ºW due to the positioning of an upper cyclone near 23ºN/56ºW. To the west of the area under investigation, a weak upper low in the eastern Gulf of Mexico is increasing the southerly flow that extends into the southeast United States. In short, all of these interacting upper level features are increasing the amount of upper level ridging off the East Coast. This pattern is somewhat similar to the pattern in which Hurricane Alex developed last season. However, Alex was caught underneath an upper ridge for several days, and the ridge enabled it to have more time to develop. This time around, the upper trough near 60ºW may steer the tropical cyclone to the northeast before another mid level steering ridge begins to slide into the western Atlantic from the central United States. With that being said, the low could rapidly develop into a moderate to strong tropical storm within 3-4 days. The SHIPS intensity model ramps up the low into a 60mph tropical storm by Day 4.
The tropical model suite will not perform with this system as well as it did with Hurricane Emily. Emily was trapped under a large subtropical ridge that did not breakdown. The tropical models can have decent verification when baroclinic (nontropical) steering features are not present; usually when the tropical cyclone is being steered by the strong low to mid level easterlies south of 25º and south of a strong subtropical ridge. There are too many baroclinic features involved with the steering off the East Coast right now. The 500MB trough near 60ºW should be the main steering factor based on global model guidance, which can be much more reliable in this situation. All of the global models are in excellent agreement so we can anticipate the consensus to verify generally well. Moreover, the current steering pattern is already setup for a track near the Carolinas, but with a significant curve to the northeast just before landfall. CIMSS 500-850MB Steering Wind Analysis shows that a weak surface ridge near 28ºN/68ºW is inducing a south-southeasterly flow along the eastern Bahamas. To the north the upper trough has enhanced the influx of westerlies streaming into the northwest Atlantic from the Great Lakes. All global models (CMC, UKMET, ECMWF, GFS, NOGAPS) indicate that the westerly flow will persist for an additional 72 hours before a mid level ridge over the Rockies propogates eastward in 96-120 hours. The developing tropical cyclone should be in the process of recurving out to sea and away from the East Coast prior to the ridge’s arrival. With the exception of 3-4 foot swells along the Carolinas and 4-5 foot swells near the Outerbanks of North Carolina the effects of the cyclone on the East Coast will be limited if the tracks verify.
The tropical wave in the western Caribbean Sea will have to be monitored for potential tropical cyclogensis in the medium range. Currently, land interaction with Honduras and the Yucatan Peninsula and upper level wind shear is putting a damper on development. An upper level low over the northern Yucatan is the main upper shear culprit, but water vapor imagery clearly shows that the feature is backing off to the west. In addition, most global models show an increase in ridging aloft over the southern Gulf of Mexico in 72 hours, which is where the wave will be located by that time. The formation of a Tropical Depression or Tropical Storm is possible in the Bay of Campeche or southwest Gulf of Mexico within approximately 60-84 hours. The steering flow will result in another trajectory similar to that of Hurricane Emily. A cyclonic flow is noted just south of Central America In the low to mid levels. This cyclonic motion will force the wave westward into the BOC/GOM within 2 days. Once in the Gulf, the wave will attempt to move northerly, but the mid level ridge progressing eastward from the Rockies to the East Coast will shun the low pressure area towards northern Mexico or southern Texas in the same manner Emily was guided westward. Initial guidances takes the low into Mexico, but the models are just beginning to pick up on the feature and some minor changes should be expected.
In the western Pacific, Tropical Storm Nalgae (07W) is forecast to remain a tropical storm throughout its lifespan. Nalgae is moving towards the northwest, and a gradual turn to the north-northeast is anticipated within the next 4 days. The latest Joint Typhoon Warning Center track would take Nalgae well to the east of Japan. As the tropical cyclone reaches the 35ºN latitude, it will begin to acquire nontropical characteristics and dissipation will soon follow. Nalgae is not expected to be a major threat to any landmasses.
Advisories on Tropical Depression 07W have also been initiated by the JTWC. In 72 hours, the JTWC is indicating further strengthening to typhoon status along with a curve to the north-northwest in the general direction of Japan. The 12Z ECMWF, NOGAPS, and GFS all take 07W relatively close to Tokyo in approximately 72 hours. If the NOGAPS and GFS solutions turn out to be correct, then 07W will pass east of Tokyo while acquiring nontropical characteristics. The ECMWF, on the other hand, depicts a continued northerly motion into Japan as a subtropical storm. It is still too early to determine the probability of a Japan landfall. Please turn to the Japan Meteorological Agency (JMA) and Joint Typhoon Warning Center (JTWC) for continuous updates.