*******Note that forecast 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.**********
...WEDNESDAY AUGUST 16 2023 1:15 PM EDT...
Mid-latitude upper ridging over the Atlantic has recently pushed upper vorticity trapped in the Atlantic tropics primarily into the western Atlantic and Caribbean. This has allowed the Atlantic tropical upper ridge... with supportive low shear and upper outflow... to recover. Currently monitoring a pair of tropical waves of low pressure taking advantage of the recovering tropical upper ridge... see area of interest #20 and #21 sections below for more information.
Elsewhere... a currently dormant tropical wave of low pressure in the eastern Caribbean may later take advantage of more favorble upper winds in the Gulf of Mexico... see area of interest #22 section below for additional details. Additional tropical areas of interest may also emerge in the Atlantic basin in the 5 to 7 day window as follows:
(1) A tropical wave of low pressure currently over central Africa is forecast to emerge into the Atlantic in about 4 days... with some model runs suggesting its development in the eastern tropical Atlantic in the 5 to 7 day window.
(2) The current Caribbean upper vorticity is forecast to fade while remaining isolated from high-latitude cold air... allowing for a more favorable upper ridge cell with low shear and outflow to develop and expand in its wake. At the surface the south part of the tropical wave associated with area of interest #22... and/or the western part of the tropical wave associated with area of interest #20... may interact with the upper ridge and produce a southern Caribbean tropical disturbance by day 7.
AREA OF INTEREST #20... A tropical wave of low pressure in the eastern Atlantic is currently stretched east to west in between 30W and 40W longitude. The NHC TAFB as of 0600Z analyzed that the wave axis was at 37.5W while the focal point of this area of interest remains an area of rotating thunderstorms now east of the wave axis positioned near 11N-34W. It is possible that the wave axis will continue westward and leave behind the rotation of interest. Forecast track points in the updated outlook below is adjusted southwestward based on the current position of the rotation... and is also adjusted to be slower for the next 48 hours as area of interest (AOI) #21 to the east is closing in on this disturbance and may tug on the disturbance and hence slow its westward track. After 48 hours AOI #21 is forecast to lessen its westward progress and bend northward which may allow this disturbance to escape its grip... thus the westward speed of this disturbance is increased after 48 hours in the outlook below. Toward the end of the 5-day forecast period... what remains of the current upper vorticity in the western Atlantic is forecast to coalesce into an upper vortex whose eastern divergence zone weakens the western part of the Atlantic surface ridge... with the forecast track bent northward toward the weakness toward days 4 and 5. Currently I am keeping peak odds of tropical cyclone formation at a low 10% as the shower and thunderstorm activity of this disturbance is disorganized. In addition AOI #21 to the east is better organized and hence may develop first... which would disadvantage this disturbance as the surface inflow and upper outflow of AOI #21 would dominate the region in this scenario.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Aug 17)... 0% chance of tropical cyclone formation (eastern tropical Atlantic near 11.5N-37.5W)
IOH 48 Hr Outlook (1200Z Aug 18)... 10% chance of tropical cyclone formation (central tropical Atlantic near 12N-40.5W)
IOH 72 Hr Outlook (1200Z Aug 19)... 10% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-45.5W)
IOH 96 Hr Outlook (1200Z Aug 20)... 10% chance of tropical cyclone formation (central tropical Atlantic near 13.5N-49W)
IOH 120 Hr Outlook (1200Z Aug 21)... 10% chance of tropical cyclone formation (central tropical Atlantic near 15.5N-51W)
****** National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT****************************
Formation chance through 48 hours...30%
Formation chance through 7 days (168 hours)...50%
AREA OF INTEREST #21... A tropical wave of low pressure that was over western Africa is emerging into the eastern tropical Atlantic while continuing to display a large gyre of showers and thunderstorms. The southwestern part of the gyre currently features a large thunderstorm mass passing south of the Republic of Cabo Verde Islands which is becoming better organized... and my updated forecast track points below are adjusted south and west accordingly. Although the updated track keeps this disurbance away from the surface ridge weakness that will soon be associated with the developing northeastern Atlantic frontal cyclone... the current mid-latitude upper ridge over the Atlantic then later the amplifying upper trough associated with the frontal cyclone will push the lingering mid-latitude upper vorticity over the eastern Atlantic southward toward this disturbance. This upper vorticity will potentially provide a northward pull in the upper layer steering... especially if this system becomes stronger/taller... and the updated forecast track below has a northward bend in the forecast track after 48 hours. At the surface... a possible fujiwhara-type interaction with Area of Interest #20 to the west may also help to heighten the northward angle of this disturbance's track. I have increased my peak odds of tropical cyclone formation to 30% in this update due to the ongoing organized thunderstorm activity of this disturbance. By days 4 and 5 I taper down the odds of development from the peak as this disturbance potentially encounters increasing westerly shear as the forecast track has this disturbance approaching the aforementioned upper vorticity.
For the Republic of Cabo Verde Islands... so far dry Saharan air has prevented activity from this tropical wave from overspreading the islands. However there is thunderstorm activity at the northern apex of the tropical wave aligned with the latitudes of the islands... therefore as the wave continues westward it is possible thunderstorm activity reaches the islands later today.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Aug 17)... 10% chance of tropical cyclone formation (eastern tropical Atlantic near 12.5N-25.5W)
IOH 48 Hr Outlook (1200Z Aug 18)... 30% chance of tropical cyclone formation (eastern tropical Atlantic near 13.5N-30W)
IOH 72 Hr Outlook (1200Z Aug 19)... 30% chance of tropical cyclone formation (eastern tropical Atlantic near 15.5N-34W)
IOH 96 Hr Outlook (1200Z Aug 20)... 20% chance of tropical cyclone formation (eastern tropical Atlantic near 18N-37.5W)
IOH 120 Hr Outlook (1200Z Aug 21)... 20% chance of tropical cyclone formation (central tropical Atlantic near 20N-40W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*****************************
Formation chance through 48 hours...20%
Formation chance through 7 days (168 hours)...40%
AREA OF INTEREST #22... A large tropical wave of low pressure has been travesing the Atlantic tropical belt and has recently arrived into the eastern Caribbean while the wave axis is now near 62W longitude. This wave has been dormant over the last few days while ingesting dry Saharan air. Recently the southeastern part of the wave has seen some increase in showers and thunderstorms moving into the southern Lesser Antilles while ventilated by the outflow of the western end of the Atlantic tropical upper ridge axis. This wave has been added into the NHC tropical weather outlook as some model runs have intermittently suggested the northern part of the tropical wave could later develop in the Gulf of Mexico in the long range... this marks the twenty-second Atlantic tropical area of interest tracked on this site this year.
The forecast track in the outlook below shows a west-northwest track across the Caribbean and into the southern Gulf of Mexico through day 5 as the tropical wave rounds the southwest extent of the Atlantic surface ridge. The tropical wave through day 3 is expected to remain largely dormant while passing beneath suppressing Caribbean and western Atlantic upper vorticity currently present. Noting that the upper ridge that was over the southeastern US has recently been split into Gulf of Mexico and Atlantic mid-latitude cells by the current eastern US upper trough. The Gulf upper ridge cell is forecast to persist... providng the wave a more favorable low shear and upper outflow environment when the northern part of its wave axis later moves into the Gulf of Mexico. For the 5-day window I have set peak odds of tropical cyclone formation at a very low 5% as computer model support developing this wave remains low... and model runs that do develop this wave do so primarily just after the current 5-day window.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Aug 17)... 0% chance of tropical cyclone formation (eastern Caribbean near 15N-67.5W)
IOH 48 Hr Outlook (1200Z Aug 18)... 0% chance of tropical cyclone formation (central Caribbean near 16N-74W)
IOH 72 Hr Outlook (1200Z Aug 19)... 0% chance of tropical cyclone formation (west of Jamaica and south of the Cayman Islands near 18N-80W)
IOH 96 Hr Outlook (1200Z Aug 20)... 0% chance of tropical cyclone formation (northwestern Caribbean near 20N-85W)
IOH 120 Hr Outlook (1200Z Aug 21)... 5% chance of tropical cyclone formation (south-central Gulf of Mexico near 22.5N-90W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT*****************************
Formation chance through 48 hours...0%
Formation chance through 7 days (168 hours)...20%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
0000Z (Aug 16) CMC Model Run...
**For area of interest #20... tropical cyclone formation suggested near 15N-38.5W at 78 hours... while in competition with area of interest #21 approaching from the northeast the tropical cyclone begins to weaken at 120 hours while located near 16.5N-41.5W
**For area of interest #21... passes over the Republic of Cabo Verde Islands at through 48 hours as a broad tropical low... the tropical low does not develop further through 120 hours while in competition with area of interest #20 while reaching 20.2N-35W
**For area of interest #22... north end of current eastern Caribbean tropical wave produces a broad tropical low in the southern Gulf of Mexico and just north of the Yucatan peninsula at 126 hours.
**South part of current eastern Caribbean tropical wave evolves into a southern Caribbean tropical low just offshore of Nicaragua by 168 hours.
**Additional tropical wave emerges from western Africa at 96 hours and evolves into a tropical cyclone near 14.8N-31W by 168 hours
0000Z (Aug 16) ECMWF Model Run...
**For area of interest #20... no development shown
**For area of interest #21... tropical wave develops a better-defined tropical low west of the Republic of Cabo Verde Islands and near 15.5N-30W at 54 hours... subsequently continues northwest to 21N-38.5W through 120 hours while evolving into a weak tropical cyclone.
**For area of interest #22... no development shown
**Additional tropical wave emerges from western Africa at 84 hours and evolves into a tropical low that reaches 15.5N-36W by 168 hours
0600Z (Aug 16) GFS Model Run...
**For area of interest #20... compact tropical cyclone formation suggested near 13N-39W at 42 hours... strengthens into a high-end compact tropical storm or hurricane through 120 hours while reaching 16N-46W
**For area of interest #21... tropical wave develops a better-defined tropical low west of the Republic of Cabo Verde Islands at 45 hours which evolves further into a large tropical storm centered near 16.5N-29.5W at 60 hours... the tropcial storm gradually weakens while also shrinking in size and reaches 19.2N-36.5W through 120 hours.
**For area of interest #22... no development shown
0000Z (Aug 16) NAVGEM Model Run...
**For area of interest #20... no development shown
**For area of interest #21... tropical wave develops a better-defined troipcal low near 15N-30W at 78 hours... tropical low reaches 16.5N-34.5W through 120 hours
**For area of interest #22... no development shown
**Additional tropical wave emerges from western Africa at 78 hours featuring a high-latitude tropical low at the Mauritania/western Sahara border... tropical low continues northwest to the waters west-southwest of the Canary Islands through 120 hours
**Additional tropical wave emerges from western Africa at 138 hours... evolves into a tropical cyclone through 168 hours centered just east-southeast of the Republic of Cabo Verde Islands.
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