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 #66

Updated: Jul 21

*******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 JULY 20 2020 7:50 PM EDT...

See area of interest sections below for disturbances being monitored for tropical cyclone formation.


AREA OF INTEREST #1...The north end of a tropical wave of low pressure that has been crossing the Caribbean Sea continues producing thunderstorm activity...currently moving throug the central Bahamas and into Cuba...while supported by split flow upper divergence between two halves of fracturing upper vorticity in the region. For this disturbance...I keep odds of development at 0% through 24 hours as this disturbance will be moving into the western of the two upper vortices. However after that time...I increase odds of development gradually to 40% as the western vortex is shown to gradually dissipate while shifting westward...increasingly placing the disturbance under favorable low shear and upper outflow beneath upper ridging extending from the southeastern United States and over very warm Gulf of Mexico water temperatures. This is slightly higher than my peak odds of 30% from yesterday as computer model support showing the disturbance developing a closed low pressure spin has increased. Surface ridging is expected to remain north of the disturbance thru the forecast period while re-enforced by the western convergence zone of a pair of shortwave upper troughs to move across north America along the US/Canada border. Therefore the forecast track is west-northwest around the south periphery of the surface ridging...but is adjusted northward during the late part of the forecast period as the latest models have the west extent of the surface ridging further east. Regardless of development...showers and vigorous thunderstorms are possible over western Cuba and southern Florida over the next 24 hours. Interests along the south Texas coast should monitor the progress of this disturbance in the next few days as it is quiet possible this disturbance develops into a tropical cyclone by then.

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

IOH 24 Hr Outlook (1800Z Jul 21)...0% chance of tropical cyclone formation (north coast of Cuba near 23N-80W)

IOH 48 Hr Outlook (1800Z Jul 22)...15% chance of tropical cyclone formation (southeastern Gulf of Mexico near 24N-85W)

IOH 72 Hr Outlook (1800Z Jul 23)...30% chance of tropical cyclone formation (central Gulf of Mexico near 25N-90W)

IOH 96 Hr Outlook (1800Z Jul 24)...40% chance of tropical cyclone formation (western Gulf of Mexico just offshore of southeast Texas and southwest Louisiana coasts near 28.5N-94W)

IOH 120 Hr Outlook (1800Z Jul 25)...0% chance of tropical cyclone formation (eastern Texas near 31.5N-96W)


AREA OF INTEREST #2...Surprisingly over the last 24 hours...a surface low pressure has spun up in the northwestern Gulf of Mexico offshore of Texas and Louisiana while featuring somehwat organized thunderstorm bands on the north and east quadrants of the circulation. Cold core upper vorticity in the Gulf and Caribbean regions has been breaking apart while remaining cut-off to the south of warm upper ridging over the southeastern United States...and this disturbance has formed from upper divergence on the northeast quadrant of a remnant upper vortex that has been sliding westward across the Gulf around the aforementioned upper ridge. ASCAT passes reveal that the surface low is not quiet closed yet...and is located at 28N-95W. Satellite imagery reveals the thunderstorms have recently weakened into more scattered cells...with no coverage over the center of low pressure due to disruption from the upper vortex. However as the upper vortex continues westward and away...I cannot rule out a burst of thunderstorms for tonight that covers the center of low pressure and strengthens this system before it makes landfall on the Texas coast in the next 12 hours...so despite the recent poor satellite presentation of this system...I have 10% odds of tropical cyclone formation instead of 0%. A northwest track into southeast Texas is expected in the next 24 hours as this system moves around the southwest periphery of the surface ridge over the southeast United States. Regardless of development or not...this system may produce heavy rainfall with isolated flash floodign over western Louisiana and southeast Texas over the next 24 hours.

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

IOH 12 Hr Outlook (0600Z Jul 21)...10% chance of tropical cyclone formation (Texas coast southwest of Galveston Bay near 29N-95.5W)

IOH 24 Hr Outlook (1800Z Jul 21)...0% chance of tropical cyclone formation (southeastern Texas near 30N-96W)


AREA OF INTEREST #3...A tropical wave of low pressure in the eastern tropical Atlantic has become better organized while developing a spiral on satellite with occasional bursts of thunderstorms. The center of the spiral is near 9N-37.5W as of this writing. This is something we have been watching for as computer models have been hinting at development in this region as previous tropical waves in the region have been able to moisten the atmosphere to the south of the dry saharan air layer...and as this region features a broad tropical upper ridge that has low shear and upper outflow conducive to tropical development. The tropical wave should continue west during the forecast period while steered by the firmly-in-place Atlantic subtropical ridge...but in the next 48 hours the westward track is expected to be slower due to the tug of a much larger tropical wave is about to emerge from the west coast of Africa (this large wave is also something recent model runs have been showing). Most models also agree that this tropical wave will generally weaken by 120 hours. I think this could be a negative effect of the large wave to the east...which looks like it could be expansive enough to push a surge of dry saharan air southwest into this tropical wave. Due to the current organization of this tropical wave and general computer model support...I give 40% odds of tropical cyclone formation in the short term...trimming them down to 20% in the longer term. At this time I do not mention potential impacts from this wave to the southern Lesser Antilles as it is unclear at this time whether this system will weaken before getting to the islands in a few days.

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

IOH 24 Hr Outlook (1800Z Jul 21)...40% chance of tropical cyclone formation (tropical Atlantic near 10N-40W)

IOH 48 Hr Outlook (1800Z Jul 22)...40% chance of tropical cyclone formation (tropical Atlantic near 10N-42.5W)

IOH 72 Hr Outlook (1800Z Jul 23)...30% chance of tropical cyclone formation (tropical Atlantic near 10N-47.5W)

IOH 96 Hr Outlook (1800Z Jul 24)...25% chance of tropical cyclone formation (tropical Atlantic near 10N-52.5W)

IOH 120 Hr Outlook (1800Z Jul 25)...20% chance of tropical cyclone formation (east-southeast of the southern Lesser Antilles 10N-57.5W)


...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 areas of interest #1 and #2...no tropical cyclone formation shown. For area of interest #3...possible tropical cyclone formation shown near 11N-47.5W in 90 hours...dissipating back into a tropical wave while moving into the southern Lesser Antilles by 138 hours. Elsewhere over the next 24 hours...shows tropical wave emerge from western Africa as a large broad tropical low pressure...loses its well defined state south of the Repubic of Cabo Verde Islands just after 48 hours without developing into a tropical cyclone.


1200Z ECMWF Model Run...For area of interest #1...surface low shown forming at 25N-90W in 48 hours....weakening to surface trough south of Louisiana in 72 hours...making landfall as a surface trough on Texas coast just after 96 hours. For areas of interest #2...no tropical cyclone formation shown. For area of interest #3...shown as a weak surface low near 10N-39W in 24 hours...opening back into a tropical wave near 45W longitude in 96 hours. Elsewhere over the next 24 hours...shows tropical wave emerge from western Africa as a large broad tropical low pressure...loses its well defined state near 45W longitude in 96 hours without developing into a tropical cyclone.


1200Z GFS Model Run...For area of interest #1...surface trough shown amplifying near 25N-90W in 54 hours...strengthens to surface low just offshore of Texas in 90 hours...makes landfall as a surface trough on the Texas coat in 96 hours. For areas of interest #2...no tropical cyclone formation shown. For area of interest #3...surface low shown opening into a tropical wave near 42W longitude in 42 hours. Elsewhere over the next 24 hours...shows tropical wave emerge from western Africa as a large broad tropical low pressure...loses its well defined state southwest of the Repubic of Cabo Verde Islands just after 48 hours without developing into a tropical cyclone.


1200Z NAVGEM Model Run...For area of interest #1...shows surface low briefly forming just south of Louisiana in 78 hours. For area of interest #2...shows surface low forming just offshore of Texas in 6 hours...making landfall shortly thereafter. For area of interest #3...shows weak surface low forming near 9N-38W in 12 hours...weakening into a tropical wave near 49W longitude in 78 hours. Elsewhere over the next 24 hours...shows tropical wave emerge from western Africa as a large broad tropical low pressure...loses its well defined state southwest of the Repubic of Cabo Verde Islands just after 48 hours....becomes better organized as a weak tropical low pressure near 13N-35W in 102 hours...loses its well-defined state near 55W in 168 hours without developing into a tropical cyclone.

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