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 #108

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


...MONDAY AUGUST 31 2020 2:56 PM EDT...

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 crossing through the eastern and central Caribbean Sea continues to show signs of organization with rotating bursts and bands of thunderstorms. My updated forecast track remains the same...which thru 72 hours shows a slow down in forward speed and a slight northward bend while the tropical wave reaches the weaker western extent of the Atlantic surface subtropical ridge...to be kept generally weaker by the surface low pressure field of the disturbance mentioned in area of interest #3 and also the frontal cyclone currently over central Canada that will slowly slide east. During the forecast period....the string of 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 sector of the aforementioned frontal cyclone...with this system expected to be between both lobes of upper vorticity. By 96 hours the western lobe will slow its westward speed while moving northward toward the upper trough associated with the central Canadian frontal cyclone. So despite surface ridging rebuilding in the wake of this frontal cyclone...I bend the forecast track more northward by 96 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. After that time...the western lobe of the upper vorticity is shown to dissipate in today's 1200Z GFS model run while starved of higher latitude colder air...and the surface ridge building in the wake of the Canadian frontal cyclone will continue to strengthen...thus this system will likely bend more westward in track assuming it survives land interaction with the Yucatan peninsula by 120 hours.


Regarding strength...this system continues to show signs of oragnization and will be in a low shear and upper outflow environment between both lobes of upper vorticity...and yet none of the models develop this system. A close examination of the last couple of days worth of 1200Z GFS model runs...in particulary today's 1200Z run...shows the culprit maybe the eastern lobe of the upper vorticity...with the GFS slingshotting some of the vorticity from this lobe southwestward directly over this system which would either induce unfavorable northeasterly shear or suppress this upper outflow of this system. My updated intensity forecast is lowered from the previous as this system has not developed into a tropical cyclone yet...and assumes it has not yet developed as its fast westward speed has prevented the south side of the circulation from fully closing off. So I wait till 48 hours to give time for a closed circulation to develop once this system slows down...and then only cautiously strengthen this system to a weak/moderate tropical storm before it makes landfall on the Yucatan peninsula due to the lackluster model support. I assume by 96 hours land interaction will cause this system to dissipate into a remnant low pressure or tropical wave. After 96 hours...even the GFS suggests upper winds becoming more favorable as the bit of upper vorticity it shows directly over this system and the western lobe of upper vorticity are both shown to dissipate...so its possible this system can develop as it turns westward across the southwestern Gulf of Mexico or Bay of Campeche by 120 hours...but for now I assume the land interaction with the Yucatan will be too much for this system to redevelop before it moves into east-central mainland Mexico such that I do not have a 120 hour forecast point.

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

0 Hr Position (1200Z Aug 31)...Tropical low pressure centered southeast of Haiti at 15.5N-71W

IOH 24 Hr Forecast (1200Z Sep 1)...Tropical low pressure centered southeast of Jamaica at 16N-76.5W

IOH 48 Hr Forecast (1200Z Sep 2)...35 mph maximum sustained wind tropical depression centered south of the Cayman Islands at 16.5N-81.5W

IOH 72 Hr Forecast (1200Z Sep 3)...50 mph maximum sustained wind tropical storm centered in the western Caribbean Sea at 17.5N-86.5W

IOH 96 Hr Forecast (1200Z Sep 4)...Remnant low pressure centered over the western Yucatan peninsula at 20N-90W


AREA OF INTEREST #2...The eastern Atlantic tropical wave of low pressure has continued moving westward and has arrived to 35W longitude while still lacking thunderstorm activity...perhaps from the dry Saharan air layer that lies to the north. Outside of the dry saharan air...conditions are favorable for this tropical wave to develop as this wave will remain under favorable upper ridging (with low shear and upper outflow) while the string of upper vorticity in the Caribbean to northeastern Atlantic breaks up into two lobes that retrograde westward and away. However the computer models are all over the place in their future ideas of this system. The CMC and ECMWF suggest this system will still stall while tugged by the tropical wave at 25W and the other tropical wave over western Africa (area of interest #4)...with all three waves merging into one. The CMC suggests this wave will be the dominant in the merger while the ECMWF favors the one over western Africa in the merger. Meanwhile the GFS suggests this wave will simply continue westward with no interaction with surrounding waves. The NAVGEM has an entirely different idea...developing the wave fragment now at 50W which was the north fracture of this tropical wave a few days ago...with this wave merging with the 50W fragment as that fragment becomes a tropical cyclone. For now...I will be going with the current observations that this system has and will continue to move westward instead of merging with the waves to the east...and will assume that dry saharan air will continue to prevent this wave from developing. Thus I have dropped my odds of tropical cyclone formation for this wave to 0%...and plan this to be my final statement on this wave on this blog unless the National Hurricane Center continues to have it in their tropical weather outlook or unless this wave later develops organized thunderstorm activity while remaining under favorable upper-level winds.

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

IOH 24 Hr Oulook (1200Z Sep 1)...0% chance of tropical cyclone formation (tropical Atlantic near 12.5N-40W)


AREA OF INTEREST #3...Thunderstorms out ahead of a cold front moving into the western Atlantic from the eastern United States have spun up into a low pressure with spiral bands...and based on this organization I have begun a tropical cyclone formation forecast as outlined below. I previously speculated that the eastern divergence zone of a shortwave upper trough to eject from a central Canada upper trough would trigger the formation of this surface low pressure...but instead it apperas the outflow of a warm upper ridge axis that extends from the Gulf of Mexico to the north Atlantic has aided in the formation of this low pressure system instead as the shortwave upper trough is currently far away from this system and in the vicinity of Illinois. Combined with the current organization of the spiral bands...this system definetely appears to be tropical in nature.


The evolution of the aformentioned shortwave upper trough energy will greatly influence the evolution of this system...and in the forecast below I am taking cues from the latest 1200Z GFS model run which is generally consistent with yesterday's 1200Z run as well. For the next 24 hours I forecast the current northeast angle in track to continue while the Illinois shortwave upper trough passes by to the north and potentially shears this system....thus I forecast only a tropical depression. By 48 hours...the 1200Z GFS shows this shortwave upper trough amplifiying into an upper vortex well to the east as the upper ridge directly over this system amplifies against the shortwave thanks to the warm sector of the frontal cyclone currently over central Canada (it is also interesting to note that the GFS suggests another tropical or subtropical cyclone developing off to the east from this upper vortex). The amplified upper ridge will reduce the shear and enhance upper outflow...and combined with the already well organized structure of this surface low pressure I forecast brisk strengthening to a strong tropical storm. I also forecast the track to bend more northward as the current northeastern United States surface ridge moves into the northwest Atlantic and temporarily blocks eastward progress of this system out to sea.


By 72 hours...another second shortwave upper trough is forecast by the GFS to eject from the central Canada upper trough and pass north of this system. I assume this system will be strong/tall enough by that point to be dragged more eastawrd in track by this second shortwave. In addition I expect the track to turn more east as the blocking northwest Atlantic surface ridge shifts eastward. I forecast rapid weakening as the track takes this system into cooler waters and northwesterly shearing upper winds between the amplififed upper ridge and southwest side of the second shortwave upper trough. Although the shear may relax by 96 hours as the second shortwave moves away and the upper ridge amplifies further...I forecast that this system will weaken further and lose its identity due to cooler water temperatures and the approach of the massive low pressure field associated with the central Canada frontal cyclone as it finally approaches.

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

0 Hr Position (1200Z Aug 31)...Low pressure centered offshore of the southeastern United States at 32.5N-77W

IOH 24 Hr Forecast (1200Z Sep 1)...35 mph maximum sustained wind tropical depression centered offshore of the southeastern United States at 33.5N-74W

IOH 48 Hr Forecast (1200Z Sep 2)...60 mph maximum susateind wind tropical storm centered offshore of the eastern United States at 37.5N-73W

IOH 72 Hr Forecast (1200Z Sep 3)...35 mph maximum sustained wind tropical depression centered offshore of the northeastern United States at 39N-69W

IOH 96 Hr Forecast (1200Z Sep 4)...Absorbed by low pressure field of frontal cyclone to the northwest while crossing 41N-64W


AREA OF INTEREST #4...A tropical wave of low pressure over interior western Africa is producing a large area of thunderstorms in the vicinity of southwestern Mali...with the thunderstorms gaining increasing banding features this afternoon suggesting a well organized low pressure spin may already be in progress with this feature. 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. Despite all of these observations...it is interesting to note that model support for this tropical wave has dropped...with the ECMWF for now being the only model that suggests some very gradual development of this system as it traverses westward across the Atlantic Ocean tropcial belt. Thus my 5-day odds of development remain on the low side given the lack of model support and the recent history of dry saharan air preventing development in the eastern tropical Atlantic...for example what happend with area of interest #2.

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

IOH 24 Hr Oulook (1200Z Sep 1)...0% chance of tropical cyclone formation (near west coast of Africa near 13N-15W)

IOH 48 Hr Outlook (1200Z Sep 2)...0% chance of tropical cyclone formation (southeast of the Republic of Cabo Verde Islands near 13N-20W)

IOH 72 Hr Outlook (1200Z Sep 3)...10% chance of tropical cyclone formation (just southwest of the Republic of Cabo Verde Islands near 13N-25W)

IOH 96 Hr Outlook (1200Z Sep 4)...20% chance of tropical cyclone formation (tropical Atlantic near 13N-30W)

IOH 120 Hr Outlook (1200Z Sep 5)...25% chance of tropical cyclone formation (tropical Atlantic near 13N-35W)


...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...no tropical cyclone formation shown. For area of interest #2...remains generally stationary near 10N-32.5W due to tug of area of interest #4...tropical cyclone formation suggested by 108 hours...in long range lifts northward while absorbing area of interest #4 located to the northeast. For area of interest #3...tropical cyclone formation suggested offshore of the Carolinas near 34.5N-74W in 36 hours....loses identity offshore of Newfoundland in advance of frontal cyclone approaching from central Canada in 114 hours. For area of interest #4...no tropical cyclone formation suggested while absorbed by area of interest #1 after 108 hours.


0000Z ECMWF Model Run...For area of interest #1...no tropical cyclone formation shown. For area of interest #2...becomes generally stationary near 10N-37.5W while tugged by area of interest #4...becomes absorbed by area of interest #4 just after 120 hours. For area of interest #3...shown to be elongated for much of the 120-hour forecast period as if its a non-tropical frontal system...loses its identity southeast of Newfoundland by 144 hours while absorbed by large low pressure field of frontal cyclone approaching from central Canada. For area of interest #4...organizes into a tropical low pressure near 17.5N-47.5W in 168 hours.


1200Z GFS Model Run...For area of interest #1...no tropical cyclone formation shown. For area of interest #2...continues westward across the Atlantic tropical belt without developing. For area of interest #3...low pressure loses identity along frontal zone while east of Cape Hatteras North Carolina in 36 hours. For area of interest #4...no tropical cyclone formation shown. Elsewhere...frontal zone tied to area of interest #3 develops a tropical cyclone in the open central Atlantic near 37.5N-47.5W in 66 hours...lifts northward in southerly flow ahead of frontal cyclone to approach from central Canada and loses its identity well east of Newfoundland in 120 hours.


0600Z NAVGEM Model Run... For areas of interest #1...tropical cyclone formation suggested just east of Belize and north of western Honduras in 90 hours...continues westward across the north-facing Bay of Campeche coast of Mexico through 120 hours. For area of interest #2...tropical wave fragment at 35W does not develop while the fragment at 50W once the north side of this wave develops into a tropical cyclone near 14N-52W in 78 hours...tropical cyclone initially stationary while both wave fragments merge. For area of interest #3...tropical cyclone formation suggested just offshore of Cape Hatteras North Carolina in 24 hours...loses its identity ahead of large frontal cyclone approaching from central Canada while located at 38.5N-57.5W in 102 hours. For area of interest #4...no tropical cyclone formation shown.

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