*******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.**********
...THURSDAY AUGUST 17 2023 11:55 PM EDT...
The Atlantic tropics remain increasingly busy while a series of tropical waves of low pressure spanning from the central Atlantic to Africa… supported by the outflow of a lengthy tropical upper ridge… are being monitored for signs of tropical cyclone formation. See area of interest #20… #21… and #23 sections below for more information.
Elsewhere... the tropical wave of low pressure currently 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.
In addition… the current Caribbean upper vorticity is currently forecast to retrograde westward and away while pushed around a recovering Gulf of Mexico upper ridge cell (refer to area of interest #22 section below for more info on the upper ridge cell)… allowing for the development of an expanding Caribbean upper ridge cell in the wake of the upper vorticity by day 4. The tropical wave of low pressure that passed 48W longitude as of 1800Z earlier today may later take advantage of this upper cell when moving into the Caribbean… and in fact this tropical wave was recently added into the NHC tropical weather outlook as a new area of interest as of 8 PM EDT. I have not yet had a chance to incorporate this new area of interest into this update cycle… will do a special update early on Friday to provide an outlook with a track forecast and probabilities of cyclone formation for this new area of interest.
AREA OF INTEREST #20... The east-to-west elongated tropical wave of low pressure that is now moving into the central tropical Atlantic has split into two features. One is the wave axis off to the west which has moved on to 46W longitude as of 1200Z and 48W as of 1800Z... and the second feature is a small tropical low pressure spin left behind by the wave axis which continues to be monitored for signs of tropical cyclone formation. The small tropical low of interest was centered near 11.5N-40W as of 1800Z based on satellite imagery which is west of the previous forecast track... indicating that area of interest (AOI) #21 to the east does not have a grip on the tropical low. Therefore for the short-term my updated forecast track shown below has a faster forward speed for the tropical low. After 48 hours the track is forecast to slow down and bend more northward due to the following... (1) 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... (2) as this system nears the upper vortex it could also be pulled northward by the vortex... especially if this system goes on to become a stronger/taller feature... (3) although the current central Canada frontal system and upper trough are not expected to affect the steering of this system... a second similar system from central Canada is forecast to break into the western Atlantic by day 5 and add to the western Atlantic surface ridge weakness. Regarding odds of development... I have raised my peak odds to 40% in this update as the tropical low has become better defined and organized. For the short-term the tropical low appears vulnerable to dry Saharan air lurking to the north and light northerly shear induced by the regional tropical upper ridge is keeping thunderstorms biased to the southern half of the circulation... however as the track curves northward and crosses directly below the upper ridge axis this shear may lessen by 72 hours which is the timeframe I place the peak odds of development. I have not selected development odds above 40% at this time as computer model support showing development has been weak as of late. By day 5 I drop development odds below the peak as the forecast track takes this system toward the southeast side of the aforementioned upper vortex where southwesterly shear would make conditions less favorable for development.
Should this system go on to develop... coastal surf generated by this system may reach the northern Lesser Antilles by day 5.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Aug 18)... 20% chance of tropical cyclone formation (central tropical Atlantic near 12N-45W)
IOH 48 Hr Outlook (1800Z Aug 19)... 30% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-50W)
IOH 72 Hr Outlook (1800Z Aug 20)... 40% chance of tropical cyclone formation (central tropical Atlantic near 14N-52.5W)
IOH 96 Hr Outlook (1800Z Aug 21)... 40% chance of tropical cyclone formation (central tropical Atlantic near 16N-54W)
IOH 120 Hr Outlook (1800Z Aug 22)... 25% chance of tropical cyclone formation (east-northeast of the northern Lesser Antilles near 18N-57W)
****** National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT****************************
Formation chance through 48 hours...40%
Formation chance through 7 days (168 hours)...50%
AREA OF INTEREST #21... The eastern Atlantic tropical wave of low pressure... which continues to feature a large gyre of showers and thunderstorms while recently passing by the Republic of Cabo Verde Islands... was initially seeing its gyre consolidate south of the islands but more recently has seen a spin tighten up toward the north... centering this system near 15N-27.5W as of 1800Z based on satellite imagery. The updated forecast track below has been adjsuted accordingly. The updated position and track now places this system closer to the developing surface ridge weakness associated with the current northeastern Atlantic frontal cyclone... which over the next 48 hours should result in a slowing of the westward track and an increase in the track's northward angle. A sluggish northwest track is then projected through 96 hours as this system becomes influenced by the same surface ridge weakness that Area of Interest #20 (AOI #20) will be bending northwards toward. Between 96 and 120 hours the track is accelerated westward... with less of a northward angle... as this system bumps into what will be remaining of the Atlantic surface ridge during that timeframe. Regarding odds of tropical cyclone formation... I have lowered peak development odds to 10% as this system currently lacks a core of organized thunderstorms while instead having scattered activity towards the periphery of its circulation... and as the northward adjusted track keeps this system closer to dry Saharan air and also westerly shear associated with the current mid-latitude eastern Atlantic upper vorticity. Although it is possible this system continues west into lower shear after 96 hours... it remains to be seen how it will negotiate the more hositle shorter term environment and so I also do not raise odds above 10% for day 5.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Aug 18)... 10% chance of tropical cyclone formation (eastern tropical Atlantic near 16N-32W)
IOH 48 Hr Outlook (1800Z Aug 19)... 10% chance of tropical cyclone formation (eastern tropical Atlantic near 17.5N-35W)
IOH 72 Hr Outlook (1800Z Aug 20)... 10% chance of tropical cyclone formation (eastern tropical Atlantic near 19N-37.5W)
IOH 96 Hr Outlook (1800Z Aug 21)... 10% chance of tropical cyclone formation (central tropical Atlantic near 20.5N-40W)
IOH 120 Hr Outlook (1800Z Aug 22)... 10% chance of tropical cyclone formation (central Atlantic near 21N-45W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT*****************************
Formation chance through 48 hours...50%
Formation chance through 7 days (168 hours)...70%
AREA OF INTEREST #22... A large tropical wave of low pressure continues to traverse westward across the eastern Caribbean. The southwest edge of the current Atlantic surface ridge is expected to push the wave west-northwest across the remainder of the Caribbean and into the Gulf of Mexico. By the end of the 5-day forecast period an amplified upper trough will be moving into eastern Canada from central Canada… with the western convergence zone of this trough building an eastern North America surface ridge. The southwest side of this ridge will continue the west-northwest trajectory of the tropical wave toward the Texas/Mexico border region. The north apex of the tropical wave has recently been able to produce showers and thunderstorms just north of the Caribbean Islands and into the eastern Bahamas with the aid of the eastern divergence zone of the upper vorticity currently in the region. Overall the wave should become dormant through 48 hours while passing directly below the suppressing upper vorticity… after which time it moves into a more favorable low shear and upper outflow environment associated with the Gulf of Mexico upper ridge cell (currently the upper ridge cell has been squashed into only the southeast corner of the Gulf by the current eastern US upper trough… however the upper ridge cell is forecast to later recover as the vorticity of the upper trough retrogrades west and away under the influence of a central US upper ridge cell). I set peak odds of tropical cyclone formation at a low 10% as model support showing development of this wave remains low.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Aug 18)... 0% chance of tropical cyclone formation (eastern Jamaica near 17.5N-76W)
IOH 48 Hr Outlook (1800Z Aug 19)... 0% chance of tropical cyclone formation (between the Cayman Islands and western Cuba near 20.5N-82.5W)
IOH 72 Hr Outlook (1800Z Aug 20)... 0% chance of tropical cyclone formation (southeastern Gulf of Mexico near 22.5N-88W)
IOH 96 Hr Outlook (1800Z Aug 21)... 5% chance of tropical cyclone formation (western Gulf of Mexico near 24N-93W)
IOH 120 Hr Outlook (1800Z Aug 22)… 10% chance of tropical cyclone formation (just north of the Texas/Mexico border near 26.2N-97.5W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT*****************************
Formation chance through 48 hours...0%
Formation chance through 7 days (168 hours)...30%
AREA OF INTEREST #23... Animation of METEOSAT satellite imagery (https://tropic.ssec.wisc.edu/real-time/europe/movies/m7irn/m7irn_loop.html) suggests a tropical wave of low pressure has moved from central to Western Africa… or from 10E longitude to 0W longitude… over a 24 hour period spanning 1800Z August 16 to 1800Z today. The tropical wave has some model support showing its development to the east of Area of Interest (AOI) #21 when it later moves into the eastern tropical Atlantic… due to the persistent favorable low shear and upper outflow of the regional tropical upper ridge to remain in place over the next several days. Therefore in this update I have added this tropical wave as an Atlantic area of interest for tropical development… the twenty-third such area of interest tracked on this site this year.
The westward forecast track has an increase in the northward angle by 96+ hours as the wave moves toward the surface ridge weakness caused by AOI #21. I set peak odds of development slightly higher than AOI #21 as the model support for this wave in the model summary below is higher than for AOI #21.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Aug 18)... 0% chance of tropical cyclone formation (western Africa near 9N-10W)
IOH 48 Hr Outlook (1800Z Aug 19)… 0% chance of tropical cyclone formation (just offshore of western Africa near 10N-16W)
IOH 72 Hr Outlook (1800Z Aug 20)… 5% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-21W)
IOH 96 Hr Outlook (1800Z Aug 21)… 15% chance of tropical cyclone formation (eastern tropical Atlantic near 12.5N-25.5W)
IOH 120 Hr Outlook (1800Z Aug 22)… 15% chance of tropical cyclone formation (eastern tropical Atlantic near 14N-30.5W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT*****************************
Not in the official outlook
…COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
1200Z (Aug 17) CMC Model Run...
**For area of interest #20... tropical cyclone formation suggested near 15.5N-46W at 42 hours... tropical cyclone stays weak while reaching 17N-55W through 120 hours
**For area of interest #21... tropical cyclone formation suggested near 20N-55W at 72 hours... weakens to a remnant low through 120 hours while reaching 21.5N-42W
**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 northwest of the Yucatan peninsula at 90 hours... tropical low continues west-northwest toward the northeast coast of Mexico through 126 hours
**For area of interest #23… tropical wave emerges from western Africa at 60 hours and evolves into a tropical cyclone just east of the Republic of Cabo Verde Islands at 90 hours... tropical cyclone moves across the islands through 108 hours and reaches 17.5N-27.5W at 120 hours
**Tropical wave currently near 48W longitude (which has recently seperated from AOI #20) evolves into a large central Caribbean tropical low centered near 16N-80.5W by 144 hours... while drifting north evolves into a large tropical cyclone centered over the Cayman Islands at 168 hours.
0000Z (Aug 17) ECMWF Model Run...
**For area of interest #20... no development shown
**For area of interest #21... tropical wave continues west-northwest as a broad tropical low whose center reaches 20N-43.8W through 120 hours.
**For area of interest #22... no development shown
**For area of interest #23… no development shown
1200Z (Aug 17) GFS Model Run...
**For area of interest #20... no development shown
**For area of interest #21... tropical wave continues west-northwest and loses its closed low pressure rotation while reaching 20N-43.5W at 120 hours.
**For area of interest #22... no development shown
**For area of interest #23… no development shown
1200Z (Aug 17) NAVGEM Model Run...
**For area of interest #20... tropical cyclone formation suggested near 16N-52.5W at 72 hours... tropical cyclone located near 16N-56W at 120 hours
**For area of interest #21... no development shown
**For area of interest #22... no development shown
**For area of interest #23... evolves into a tropical cyclone centered over the southern Republic of Cabo Verde Islands through 132 hours
**Tropical wave currently near 48W longitude (which has recently seperated from AOI #20) evolves into a central Caribbean tropical low near 14N-78.5W at 132 hours
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