BIRDSEYE VIEW POSTS

Since 2012 on the Weather Underground (www.wunderground.com) blogs, I have been posting annotated "birdseye view" charts of the Atlantic basin, with a detailed explanation and forecasting that references the chart. From there you may know me as "NCHurricane2009." While I now do these "birdseye view" posts here, I will continue to do comments via Disqus on Weather Underground at www.wunderground.com/cat6. You can see my Disqus feed at this link for my latest comments. Feel free to reply to me with your disqus account or e-mail at IOHurricanes@outlook.com 

 
 
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MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #107

*******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.**********

...SUNDAY AUGUST 30 2020 11:45 PM EDT...

Satellite image (as of 0300Z) showing all areas of interest being monitored for development in yellow circles:


NHC TAFB Surface Analysis from 1800Z:

GFS Model Upper Level Winds from 1800Z:


See area of interest sections below for all areas of interest being monitored for tropical cyclone formation over the next few days.

AREA OF INTEREST #1...The tropical wave of low pressure from the central tropical Atlantic has crossed the Lesser Antilles and entered the eastern Caribbean Sea while becoming considerably better organized with spiral thunderstorm bands. Therefore I have begun a tropical cyclone formation forecast as outlined below. This system is continuing faster to the west than I previously forecast...therefore my updated forecast track is adjusted westward accordingly. For the next 96 hours I forecast the track of this system to slow and bend more northward while it reaches the weaker western extent of the Atlantic surface subtropical ridge...to be kept generally weaker by a pair of frontal cyclones (the current one over eastern North America...the second one to develop later and over Canada). During the forecast period....the stretched upper vorticity spanning the Caribbean Sea to central and northeast Atlantic is expected to consolidate into two lobes of upper vorticity that retrograde westward around high-latitude upper ridging to be induced by the warm sectors of the aforementioned frontal cyclones...with this system expected to be between both lobes of upper vorticity. By 120 hours the western lobe will slow its westward speed while moving northward toward the upper trough associated with the forecast Canadian frontal cyclone. So despite surface ridging rebuilding in the wake of this frontal cyclone...I bend the forecast track more northward by 120 hours as I assume this system will be strong/tall enough to be dragged by the western lobe of upper vorticity while it catches up to it.

Regarding strength...this system is already well organized and will be in a low shear and upper outflow environment between both lobes of upper vorticity...and yet none of the models in today’s 1200Z cycle develop this system. Thus I only gradually raise the forecast intensity to strong tropical Storm status by 96 hours before landfall with the Yucatan peninsula of Mexico...followed by weakening due to land interaction with the peninsula.

******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********

0 Hr Position (1800Z Aug 30)...Tropical low pressure centered in the eastern Caribbean Sea at 15N-65W

IOH 24 Hr Forecast (1800Z Aug 31)...35 mph maximum sustained wind tropical depression centered south of Haiti at 15.5N-72W

IOH 48 Hr Forecast (1800Z Sep 1)...45 mph maximum sustained wind tropical storm centered south of Jamaica at 16N-77.5W

IOH 72 Hr Forecast (1800Z Sep 2)...60 mph maximum sustained wind tropical storm centered south of the Cayman Islands at 16.5N-82.5W

IOH 96 Hr Forecast (1800Z Sep 3)...70 mph maximum sustained wind tropical storm centered just offshore of the east Yucatan peninsula coast of Mexico at 17.5N-87.5W

IOH 120 Hr Forecast (1800Z Sep 4)...40 mph maximum sustained wind tropical storm centered in the eastern Bay of Campeche just offshore of the western Yucatan peninsula at 20N-91W

AREA OF INTEREST #2...The eastern Atlantic tropical wave of low pressure has continued moving westward and has arrived to 30W longitude while showing reduced thunderstorm activity...perhaps from the dry Saharan air layer that lies to the north. The CMC model suggests this wave will slow down while merging with the other wave to the east that has recently emerged from Africa...located at 20W...while the GFS suggests this wave will simply continue westward. With the latest satellite animation suggesting this tropical wave slowing down perhaps while gravitated toward the wave at 20W...I have adjusted my forecast points westward due to the current 30W position of this wave but also show an initially slower westward track. My strategy is to compromise between the faster GFS and slower CMC until it is clear which idea will be the correct one. My updated outlook has a lower 5-day peak odds of development at 20% compared to my previous...due to the reduced thunderstorms and increasingly reduced computer model support.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1800Z Aug 31)...0% chance of tropical cyclone formation (tropical Atlantic near 12.5N-32W)

IOH 48 Hr Oulook (1800Z Sep 1)...0% chance of tropical cyclone formation (tropical Atlantic near 12.5N-34W)

IOH 72 Hr Outlook (1800Z Sep 2)...5% chance of tropical cyclone formation (tropical Atlantic near 12.5N-37W)

IOH 96 Hr Outlook (1800Z Sep 3)...10% chance of tropical cyclone formation (tropical Atlantic near 12.5N-42W)

IOH 120 Hr Outlook (1800Z Sep 4)...20% chance of tropical cyclone formation (tropical Atlantic near 12.5N-47W)

AREA OF INTEREST #3...Computer models continue to agree that the cold front currently heading into the Atlantic from the eastern United States will develop a pocket of low pressure when the front moves into the western Atlantic capable of tropical cyclone formation. The enablers for tropical development will be warm Gulf Stream waters and warm upper ridging (with low shear and upper outflow) expanding from the Gulf of Mexico and into the northwest Atlantic thanks to the warm sector of a frontal cyclone to develop over Canada during the forecast period. The eastern divergence zone of shortwave upper trough energy to separate from the Canadian frontal cyclone’s longwave upper trough appears to be what will trigger the pocket of low pressure along the tail end of the front once it moves into the Atlantic. The evolution of this shortwave energy is uncertain and will greatly influence the evolution of this system. Yesterday the 1200Z GFS suggests the energy would amplify into a solid vortex while the northwest Atlantic upper ridging amplified around it...but today’s 1200Z GFS suggests the energy would come as multiple low amplitude troughs. Perhaps multiple models are agreeing with todays 1200Z GFS as many of them are shifting westward in track ...less indicative of an upper vortex pushing this system east and more indicative that this system will thus be blocked by a surface ridge to build in the northwest Atlantic under the western convergence zone of this fronts upper trough. Thus my forecast points are adjusted westward...and also southward as the stronger thunderstorm activity ahead of the front is currently further south.

I have raised my odds of tropical cyclone formation to 70% as most of the models now show this system having tropical characteristics. Curiously the GFS which yesterday had this system as a strong tropical cyclone now has the weakest presentation for this system today...perhaps because it sees the multiple shortwave troughs shearing this system which would be a negative for tropical development. Thus my 96 and 120 hour odds of development are below 70% in case this system indeed deals with shear from multiple shortwave troughs later on.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1800Z Aug 31)...10% chance of tropical cyclone formation (just offshore of the Carolinas near 33N-75W)

IOH 48 Hr Oulook (1800Z Sep 1)...70% chance of tropical cyclone formation (western Atlantic near 35N-71W)

IOH 72 Hr Outlook (1800Z Sep 2)...70% chance of tropical cyclone formation (western Atlantic near 37N-66W)

IOH 96 Hr Outlook (1800Z Sep 3)...50% chance of tropical cyclone formation (northern Atlantic near 38N-59W)

IOH 120 Hr Outlook (1800Z Sep 4)...30% chance of tropical cyclone formation (northern Atlantic near 39N-54W)

AREA OF INTEREST #4...A tropical wave of low pressure over interior Western Africa is producing a curved band of thunderstorms in the vicinity of 13N-6W. The GFS since yesterday suggested this wave would develop as it emerges from Africa and into the eastern Atlantic...and the CMC and ECMWF are joining the GFS today. Therefore the National Hurricane Center has already introduced this wave into their tropical weather outlook. This wave will remain under favorable upper ridging (with low shear and upper outflow) during the forecast period as the string of upper vorticity in the Caribbean to northeastern Atlantic breaks up into two lobes that retrograde westward and away. However I only have my peak 5 day odds of development at 20% at this time as dry Saharan air has had a recent history of preventing development in the eastern Atlantic...for example what we are seeing now with area of interest #2.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1800Z Aug 31)...0% chance of tropical cyclone formation (western Africa near 13N-11W)

IOH 48 Hr Oulook (1800Z Sep 1)...0% chance of tropical cyclone formation (near west coast of Africa near 13N-16W)

IOH 72 Hr Outlook (1800Z Sep 2)...0% chance of tropical cyclone formation (southeast of the Republic of Cabo Verde Islands near 13N-21W)

IOH 96 Hr Outlook (1800Z Sep 3)...10% chance of tropical cyclone formation (just southwest of the Republic of Cabo Verde Islands near 13N-26W)

IOH 120 Hr Outlook (1800Z Sep 4)...20% chance of tropical cyclone formation (tropical Atlantic near 13N-31W)

...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)

1200Z CMC Model Run...For area of interest #1...no tropical cyclone formation shown. For area of interest #2...tropical cyclone formation suggested near 10N-36W in 120 hours. For area of interest #3...tropical cyclone formation suggested offshore of the Carolinas near 34.5N-74W in 48 hours....loses identity offshore of Nova Scotia in advance of frontal cyclone approaching from Canada in 120 hours. For area of interest #4...organizes into a tropical low pressure over the Republic of Cabo Verde Islands in 120 hours.

1200Z 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...tropical cyclone formation suggested near 37.5N-68W by 72 hours....transitions to elongated non-tropical low pressure near 37N-60.5W in 96 hours. For area of interest #4...organizes into a tropical low pressure just west of the Republic of Cabo Verde Islands in 120 hours.

1200Z GFS Model Run...For area of interest #1...organizes into low pressure spin in Bay of Campeche in 168 hours. For area of interest #2...organizes into a tropical low pressure east of the Lesser Antilles in 138 hours. For area of interest #3...small weak low pressure develops southeast of Cape Hatteras North Carolina in 48 hours...transitions to elongated non-tropical frontal low near 36.5N-60W by 114 hours. For area of interest #4...tropical cyclone formation suggested near 10N-23W by 120 hours.

1200Z NAVGEM Model Run... For areas of interest #1 and #2...no tropical cyclone formation shown. For area of interest #3...tropical cyclone formation suggested near 35N-73W in 54 hours...strong tropical cyclone suggested near 37.5N-55W in 120 hours. For area of interest #4...no tropical cyclone formation shown.

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