*******Note that forecasts and outlooks in this post are NOT the official forecast from the National Hurricane Center (NHC). They are my own detailed views on the Atlantic tropics based on current observations and latest computer model runs. As such do not make decisions based on my posts...consult news media...watches and warnings from your local weather office...and any evacuation orders issued by local governments to make the most informed and best decisions. Visit the NHC website hurricanes.gov (hurricanes dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********
...TUESDAY AUGUST 18 2020 2:14 PM EDT...
See area of interest #3 section below for an update on the remnants of Tropical Storm Josephine. Also see area of interest #1...#2...and #4 sections below for central and eastern Atlantic tropical waves of low pressure being monitored for development. Elsewhere...the southern portion of the large upper trough over eastern North America is expected to become cut-off in the Gulf of Mexico due to an amplifying upper ridge over western North America. The chances of this cut-off upper trough triggering a subtropical or tropical disturbance in the Gulf of Mexico with its eastern divergence zone are low as the disturbance mentioned in area of interest #1 will likely dominate the region.
AREA OF INTEREST #1...The central Atlantic tropical wave of low pressure has crossed the Lesser Antilles and entered the southeastern Caribbean Sea. Although the tropical wave has some signs of organization on satellite pictures with curved bands of thunderstorms appearing at times...it appears to have a somewhat broad circulation. In fact the western part of the broad tropical wave has become better organized this morning offshore of the northeastern Venezuela coast...prompting me to shift my forecast track points southwestward. Due to the current organization of the tropical wave and ongoing computer model support from the GFS...NAVGEM...and CMC computer models showing development...I have begun a tropical cyclone formation forecast as outlined below.
This tropical wave will remain tucked beneath a cell of upper ridging thru the forecast period which will provide favorable low shear and upper outflow for potential tropical development. Therefore the only inhibiting factor for development will be the tropical wave's structure. Due to the current broad structure...I wait till 48 hours before forecasting tropical cyclone formation and then have an initial gradual strengthening rate through 72 hours to give this system some time to consolidate. After that time...I forecast more brisk strengthening...bringing this system to a high end category 1 hurricane by the end of the forecast period. The south part of the longwave upper trough over eastern North America will become cut-off over the Gulf of Mexico due to the strength of an upper ridge over western North America...and I bend the forecast track increasingly northwestward by 96 and 120 hours as I assume this system will be a strong/tall enough tropical cyclone to be dragged by the upper trough. I do not show a complete turn to the north (i.e. still have some westward component to the forecast track through 120 hours) as the cut-off upper trough is shown to start weakening in the GFS model run late in the forecast period...perhaps the effects of staying cut-off from high latitude upper troughs that would otherwise re-energize it with cooler air...and perhaps from the latent heat release of this system's thunderstorms also weakening the cut-off upper trough should it indeed become a strengthening hurricane. Because the cut-off upper trough and its shearing upper westerly winds will be weakening...this would allow for strenghtening to continue unabated as this system enters the Gulf of Mexico. And combined with the rather warm 30 deg C Gulf of Mexico waters... there is a possiblity of this system becoming a rather strong hurricane just after the forecast period...we shall see in the coming days.
Interests in Jamaica...Cayman Islands...western Cuba...and the Yucatan peninsula of Mexico should continue to carefully monitor the progress of this tropical wave. It appears the southwestward shift in the forecast track has reduced the threat of direct impacts to Jamaica and the Cayman Islands...but some peripherial impacts from the northern rain bands of this system cannot be ruled out should the forecast track shift again as this broad sysetm consolidates.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Aug 18)...Tropical low pressure centered in the southeastern Caribbean Sea at 12.5N-65W
IOH 24 Hr Forecast (1200Z Aug 19)...Tropical low pressure centered offshore of the northwestern Venezuela coast at 14N-70W
IOH 48 Hr Forecast (1200Z Aug 20)...35 mph maximum sustained wind troipcal depression centered in the central Caribbean Sea at 15N-75W
IOH 72 Hr Forecast (1200Z Aug 21)...50 mph maximum sustained wind tropical storm centered in the central Caribbean Sea at 16N-80W
IOH 96 Hr Forecast (1200Z Aug 22)...75 mph maximum sustained wind hurricane centered in the western Caribbean Sea at 18.5N-84.5W
IOH 120 Hr Forecast (1200Z Aug 23)...95 mph maximum sustained wind hurricane centered just offshore of the northeastern Yucatan peninsula at 21N-86W
AREA OF INTEREST #2...The thunderstorm activity of the tropical wave of low pressure in the far eastern Atalntic apperas to be increasingly becoming a very thick northeastern outer band feeding the organizing tropical low pressure to the west-southwest (area of interest #4). The National Hurricane Center no longer has this tropical wave in its tropical weather oulook...instead the tropical low pressure to the west is now in the outlook. Based on the aforementioed satellite observations...it appears this disturbance will gradually merge with the tropical low pressure to the west...therefore I am dropping this disturbance's odds of tropical cyclone formation to 0%. This is my final statement on this disturbance on this blog unless it somewhow retains its identity and re-organizes.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Aug 19)...0% chance of tropical cyclone formation (tropical atlantic near 14N-35W)
AREA OF INTEREST #3 (REMNANTS OF JOSEPHINE)...The remnants of Tropical Storm Josephine continue as a surface trough of low pressure that has been curiously stationary in the vicinity of 25N-68W over the last 24 hours instead of continuing north around the west side of the steering Atlantic subtropical ridge. This places the remnants in westerly shearing flow south of a pair of western Atlantic upper vortices instead of the calmer lower shear winds in between the upper vortices located to the north. In addition the thunderstorm activity associated with the remnants continue to be lacking...and it could very well be dissipating. Therefore I have lowered the odds of tropical cyclone formation to 0%...this is my final statement on Josephine's remnants on this blog.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Aug 19)...0% chance of tropical cyclone formation (western Atlantic near 27.5N-68W)
AREA OF INTEREST #4...A tropical wave of low pressure in the eastern tropical Atlantic now in the vicnity of 45W longitude has left behind a continuously organizing tropical low pressure in the vincity of 12N.5N-40W. Due to increasing organization of the tropical low pressure's thunderstorm bands...I have begun a tropical cyclone formation forecast as outlined below.
This tropical low pressure will remain in a favorable low shear and upper outflow environment beneath a very lengthy tropical upper ridge axis during much of the forecast period...so the only inhibiting factor for development will be the structure of the tropical low and any instrusions of dry saharan air to the north. My assumption in my forecast below is that this system will soon merge with the other tropical disturbance to the east-northeast (area of interest #2)...resulting in a southwest-to-northeast broad circulation that gradually consolidates somewhere in the middle...thus my forecast points are lifted northward...with a more westward track around the south side of the Atlantic subtropical surface ridge resuming after 48 hours after the broad system consolidates. The northward adjusted forecast track points are also in agreement with the latest model consensus...so perhaps the models agree with this idea. With this paradigm...I show only slow strengthening into a tropical depression and then tropical storm as this system will need time to consolidate before more brisk strengthening can occur. I also assume the dry saharan air to the north will not affect this system as the large circulation will create quiet a large moisture field. Later in the forecast period...the strength of this system will depend on exactly how the cut-off upper vortex currently in the central Atlantic evolves. The GFS suggests some of this upper vorticity will become streteched southwestward toward the eastern Caribbean region by the robust northwestern Atlantic upper ridge to persist in warm southerly flow ahead of the frontal zone currently exiting the eastern United States coast. My assumption is that the tremendous latent heat release of this large system will break through any of the cold core upper vorticity that moves toward the eastern Caribbean...allowing the tropcial upper ridge axis to merge with the sprawling northwestern Atlantic upper ridge such that this system will be allowed to continue strengthening in a low shear and upper outflow environment. Curiously the GFS does not develop this system much...perhaps while assuming the upper vorticity will disrupt this system and maybe also from the dry saharan air layer that lurks to the north. Thus with some uncertainty on exactly how favorable the enviroment will be late in the forecast period...I cautiously bring the intensity into category 1 hurricane strength.
Due to the favorable outlook for this system to develop and current forecast track...interests in the Lesser Antilles...Virgin Islands...and Puerto Rico are advised to watch this system carefully over the next few days.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Aug 18)...Tropical low pressure centered at 12.5N-40W
IOH 24 Hr Outlook (1200Z Aug 19)...35 mph maximum sustained wind tropical depression centered at 14N-44W
IOH 48 Hr Outlook (1200Z Aug 20)...40 mph maximum sustained wind tropical storm centered at 15.5N-48W
IOH 72 Hr Outlook (1200Z Aug 21)...50 mph maximum sustained wind tropical storm centered at 16N-54W
IOH 96 Hr Outlook (1200Z Aug 22)...70 mph maximum sustained wind tropical storm centered just east of the northern Lesser Antilles at 17N-60W
IOH 120 Hr Outlook (1200Z Aug 23)...85 mph maximum sustained wind hurricane centered just north of the Virgin Islands at 19N-65W
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
0000Z CMC Model Run...For area of interest #1...tropical cyclone formation suggested just east of Belize and north of Honduras in 102 hours...weakens to a remnant low over the Yucatan peninsula at 120 hours due to landfall. For area of interest #2...no tropical cyclone formation shown. For area of interest #3 (remnants of Josephine)...no tropical cyclone formation shown. For area of interest #4...shown to become a tropical cyclone at 16N-46.5W in 54 hours...passes just north of the northern Lesser Antilles as a compact strengthening tropical cyclone in 108 hours...centered just offshore of the northeastern Dominican Republic coast as a possibly intense tropical cyclone in 126 hours.
0000Z ECMWF Model Run...For area of interest #1...no tropical cyclone formation shown. For area of interest #2...no tropical cyclone formation shown. For area of interest #3 (remnants of Josephine)...no tropical cyclone formation shown. For area of interest #4...tropical cyclone formation suggested at 12.5N-41W in 24 hours...passes just north of the northern Lesser Antilles in 96 hours...moving into the eastern Bahamas in 120 hours (no strengthening shown from 24 to 120 hours). Elsewhere...large tropical wave emerges from western Africa into the eastern tropical Atlantic in 72 hours...tropical cyclone formation suggested west of the Republic of Cabo Verde Islands near 16.5N-26.5W in 120 hours.
0600Z GFS Model Run...For area of interest #1...tropical wave organizes into a tropical low pressure east of Nicaragua in 78 hours...tropical cyclone formation suggested east of Belize and north of Honduras in 96 hours...makes landfall on east coast of the Yucatan peninsula of southeastern Mexico as a compact strengthening tropical cyclone in 120 hours. For area of interest #2...no tropical cyclone formation shown. For area of interest #3 (remnants of Josephine)...no tropical cyclone formation shown. For area of interest #4...tropical wave organizes into a tropical low pressure over the northern Lesser Antilles in 96 hours...opens back into a tropical wave over western Puerto Rico in 108 hours.
0600Z NAVGEM Model Run...For area of interest #1...tropical cyclone formation suggested on the northeast coast of the Yucatan peninsula in 126 hours...curves northward into central Gulf of Mexico in longer range. For area of interest #2...no tropical cyclone formation shown. For area of interest #3 (remnants of Josephine)...no tropical cyclone formation shown. For area of interest #4...tropical cyclone formation suggested near 19N-54W in 72 hours...located in the western Atlantic near 22.5N-62.5W in 120 hours.
Comments