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 #93

*******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 17 2020 12:50 AM EDT...


Tropical Storm Josephine has weakened to a remnant low pressure area north of Puerto Rico...see area of interest #3 section below for an update on the remannts of Josephine as I am watching it for potential redevelopment as it curves northward toward Bermuda over the next couple of days. Also see area of interest #1 and #2 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. This cut-off upper trough may trigger a subtropical or tropical disturbance in the Gulf of Mexico with its eastern divergence zone in the next few days...with the tail end of the current front over the eastern United States possibly providing a surface low pressure field for this disturbance.


AREA OF INTEREST #1...The central Atlantic tropical wave of low pressure has seen an increase in thunderstorms as it moves westward away from the dry saharan air that has been in greater concentraionts further to the east. However the thunderstorm activity has grown increasingly disorganized tonight...therefore I have lowered the shorter term odds of tropical cyclone formation from this system. 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...and the GFS and NAVGEM have joined the CMC model in showing development of this tropical wave as it moves across the Caribbean Sea. Therefore I have notably raised my odds of tropical cyclone formation in the longer range. Regarding the forecast track...the upper trough over eastern North America and its associated surface cold front over the eastern United States are currenty forecast to pass too far north to weaken the steering Atlantic subtropical ridge. Therefore a steady west-northwest track across the Lesser Antilles and into the Caribbean Sea...perhaps approaching Jamaica by day 5...appears likely. After 5 days...it appears a south fracture of the eastern North America upper trough will linger in the Gulf of Mexico for quiet some time while cut-off by an amplified upper ridge over western North America...with this cut-off trough's eastern divergene zone keeping low surface pressures in the Gulf of Mexico. Therefore it appears this low pressure field is likely to draw this system northwestward toward the Gulf of Mexico in the long range after 5 days.

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

IOH 24 Hr Outlook (1800Z Aug 17)...5% chance of tropical cyclone formation (East of Lesser Antilles near 13N-56.5W)

IOH 48 Hr Outlook (1800Z Aug 18)...15% chance of tropical cyclone formation (eastern Caribbean Sea near 13.5N-62W)

IOH 72 Hr Outlook (1800Z Aug 19)...30% chance of tropical cyclone formation (eastern Caribbean Sea near 14N-67.5W)

IOH 96 Hr Outlook (1800Z Aug 20)...45% chance of tropical cyclone formation (central Caribbean Sea south of Haiti near 15N-72.5W)

IOH 120 Hr Outlook (1800Z Aug 21)...65% chance of tropical cyclone formation (central Caribbean Sea just southwest of Jamaica near 16N-78W)


AREA OF INTEREST #2...The tropical wave of low pressure that has recently exited the west African coast with a large field of vigorous thunderstorms has increasingly become disorganized while its north half has been disrupted by dry saharan air. However...I have introduced this wave as an area of interest for tropical development as the National Hurricane Center has added it to its tropical weather outlook in the last 24 hours. I keep odds of development toward the low side due to the ongoing prevalance of dry saharan air in the eastern and central tropical Atlantic where this tropical wave will be traversing thru the 5-day forecast period (while steered by the Atlantic surface subtropical ridge). Another reason I keep odds low is only the ECMWF has joined the CMC in forecasting this wave to develop. Other than the dry saharan air...conditions are favorable for this tropical wave to develop as the tropical wave will be embedded beneath tropical upper ridging providing low shear and upper outflow.

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

IOH 24 Hr Outlook (1800Z Aug 17)...0% chance of tropical cyclone formation (tropical atlantic near 10N-26W

IOH 48 Hr Outlook (1800Z Aug 18)...10% chance of tropical cyclone formation (tropical atlantic near 11N-32W

IOH 72 Hr Outlook (1800Z Aug 19)...15% chance of tropical cyclone formation (tropical atlantic near 11.5N-37W)

IOH 96 Hr Outlook (1800Z Aug 20)...20% chance of tropical cyclone formation (tropical atlantic near 12N-43W)

IOH 120 Hr Outlook (1800Z Aug 21)...25% chance of tropical cyclone formation (tropical atlantic near 12.5N-50W)


AREA OF INTEREST #3 (REMNANTS OF JOSEPHINE)...Tropical Storm Josephine has weakened to a remnant low pressure area north of Puerto Rico due to westerly shear induced by an upper trough in the western Atlantic. The remannt low pressure field...if it persists...will curve northward toward Bermuda while steered in the flow ahead of the frontal zone approaching from the eastern United States and around the west side of the Atlantic surface subtropical ridge. Upper winds could become more conducive for redevelopment of Josephine in 48 hours as the cold core western Atlantic uppper trough breaks apart and weakens due to warm southerly flow ahead of the approaching fronal zone. By 72 hours shear may start to re-increase as the longwave upper trough over eastern North America approaches...but I keep some non-zero odds of development during that time as the shear may still be light enough to not completely shut off development potential. But by 96 hours the shear will likey increase further...thus I drop the odds of development to 0%. I keep my peak odds of development at a low 10% due to the current lack of thunderstorms with this system on infrared satellite...and also due to weak comptuer model support (with only intermittent runs of the less reliable NAVGEM and CMC showing devlopment).

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

IOH 24 Hr Outlook (1800Z Aug 17)...0% chance of tropical cyclone formation (western Atlantic near 25N-68.5W)

IOH 48 Hr Outlook (1800Z Aug 18)...10% chance of tropical cyclone formation (southwest of Bermuda near 29N-67.5W)

IOH 72 Hr Outlook (1800Z Aug 19)...10% chance of tropical cyclone formation (over Bermuda near 32N-65W)

IOH 96 Hr Outlook (1800Z Aug 20)...0% chance of tropical cyclone formation (northeast of Bermuda near 34N-61W)


...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...tropical cyclone formation suggested just north of eastern Honduras in 132 hours. For area of interest #2...tropical cyclone formation suggested just east of the northern Lesser Antilles in 126 hours. For area of interest #3 (remnants of Josephine)...no tropical cyclone formation shown. Elsewhere...tail end of frontal zone currently over the eastern United States decays into broad low pressure in the central Gulf of Mexico in 72 hours...nearly stationary tropical disturbance suggested through 138 hours that drifts into western Gulf of Mexico...by 144+ hours disturbance loses definition to area of interest #1 as it become the dominant tropical cyclone in the region.


1200Z ECMWF Model Run...For area of interest #1...no tropical cyclone formation shown. For area of interest #2...tropical cyclone formation suggested at 16N-50W in 96 hours...located east-northeast of the northern Lesser Antilles at 120 hours. For area of interest #3 (remnants of Josephine)...no tropical cyclone formation shown.


1800Z GFS Model Run...For area of interest #1...tropical wave organizes into a tropical low pressure north of Honduras in 132 hours. For area of interest #2...no tropical cyclone formation shown. For area of interest #3 (remnants of Josephine)...no tropical cyclone formation shown.


1800Z NAVGEM Model Run...For area of interest #1...tropical cyclone formation suggested between the Cayman Islands and western Cuba in 132 hours. For area of interest #2...no tropical cyclone formation shown. For area of interest #3 (remnants of Josephine)...no tropical cyclone formation shown.

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