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 #67

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


...TUESDAY JULY 21 2020 1:07 PM EDT...

See area of interest sections below for disturbances being monitored for tropical cyclone formation. Elsewhere...a large tropical wave exiting the west coast of Africa into the eastern tropical Atlantic has seen a decrease in thunderstorms while it begins to push a swath of dry saharan air southwestward into the region of the Atlantic it will soon move into. Not considering this tropical wave an area of interest for development at the present time as it appears the dry air has already begun to weaken the thunderstorm activity of the wave compared to yesterday.


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 through the Cayman Islands...western Cuba...and the south tip of Florida...while supported by a spot of low shear and enhanced upper outflow in between two lobes of upper vorticity in the region. For this disturbance...I have slightly lowered short-term odds of development as the thunderstorm activity is still not organized around a surface spin...while the spin seen toward the west edge of the activity is associated with the western of the two lobes of upper vorticity that continues to disrupt this disturbance. But I still increase odds of development gradually to 40% as the western lobe of upper vorticity is shown in the models 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. Surface ridging is expected to remain north of the disturbance thru the forecast period while re-enforced by the western convergence zone of upper troughs moving across north America along the US/Canada border. Therefore the forecast track is west-northwest around the south periphery of the surface ridging...followed by a northwest turn into eastern Texas as the disturbance reaches the west side of the ridge. Regardless of development...showers and vigorous thunderstorms are possible over western Cuba...the Cayman Islands...and southern Florida today. Interests along the south Texas coast should monitor the progress of this disturbance in the next few days as it is still 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 (1200Z Jul 22)...5% chance of tropical cyclone formation (southeastern Gulf of Mexico near 24N-85W)

IOH 48 Hr Outlook (1200Z Jul 23)...25% chance of tropical cyclone formation (central Gulf of Mexico near 25N-90W)

IOH 72 Hr Outlook (1200Z 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 96 Hr Outlook (1200Z Jul 25)...0% chance of tropical cyclone formation (eastern Texas near 31.5N-96W)


AREA OF INTEREST #2...The northwestern Gulf of Mexico surface low pressure that was triggered by the upper divergence zone on the northeast periphery of an upper vortex that has been sliding westward into northern Mexico from southern Texas has made landfall as a surface trough along the Texas coast...and will continue northwestward inland while steered around surface ridging over the eastern United States. Thunderstorm activity has increased overnight while the departing upper vortex has allowed for upper ridging/supporting outflow over the southeastern United States to build over the disturbance. However tropical cyclone development is no longer possible due to land interaction...but based on the latest radar imagery heavy rainfall with isolated flash flooding is a possiblity today over parts of southeastern Texas. This is my final statement on this disturbance as it is not expected to become a tropical cyclone.

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

IOH 12 Hr Outlook (0000Z Jul 22)...0% chance of tropical cyclone formation (southeastern Texas near 30.5N-96.5W)


AREA OF INTEREST #3...The central tropical low pressure spin seeded from a broad tropical wave of low pressure that exited Africa a few days ago has continued to maintain organization with central bursts of thunderstorms and spiral bands around the central bursts...therefore it appears a tropical depression is forming and I have begun a tropical cyclone formation forecast as outlined below. This system should continue west toward the southern Lesser Antilles islands during the forecast period while steered by the firmly-in-place Atlantic subtropical ridge. Regarding strength...conditions in the short-term are quiet favorable due to low shear and upper divergence provided by a broad tropical upper ridge in the region...therefore I forecast this system to become a moderate strength tropical storm in the next 24 hours. Computer models continue to agree that this system will weaken back to a tropical wave by the time it reaches the southern Lesser Antilles. It appears based on the imposing large swath of dry saharan air seen just to the north...that this could be due to the large tropical wave currently exiting Africa capable of pushing this dry air southwest into this system. Therefore my intensity forecast gradually weakens this system to a tropical wave after 24 hours. At this time I do not mention potential impacts from this system to the southern Lesser Antilles as it is unclear whether this system will have vigor by the time it reaches this area.

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

0 Hr Position (1200Z Jul 21)...Surface low centered at 9.5N-39.5W

IOH 24 Hr Forecast (1200Z Jul 22)...50 mph maximum sustained wind tropical storm centered at 10N-42W

IOH 48 Hr Forecast (1200Z Jul 23)...50 mph maximum sustained wind tropical storm centered at 10N-47W

IOH 72 Hr Forecast (1200Z Jul 24)...45 mph maximum sustained wind tropical storm centered at 10N-52W

IOH 96 Hr Forecast (1200Z Jul 25)...35 mph maximum sustained wind tropical depression centered east-southeast of the Lesser Antilles at 10.5N-57W

IOH 120 Hr Forecast (1200Z Jul 26)...Remnant tropical wave located in the southeastern Caribbean Sea just north of the Venezuela coast at 62W longitude


...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...surface low shown to form near 25N-92W in 42 hours...makes landfall on the southern Texas coast as a weakening surface trough in 84 hours. For area of interest #2...no tropical cyclone formation shown. For area of interest #3...possible compact tropical cyclone shown near 10N-45W in 54 hours...dissipating back into a tropical wave while nearing the Lesser Antilles in 132 hours. Elsewhere...the current large tropical wave emerging from western Africa is shown to become better organized into a tropical low pressure near 12N-35W in 138 hours.


0000Z ECMWF Model Run...For area of interest #1...surface low shown forming at 25N-91W in 48 hours...making landfall as a surface trough on south Texas coast at 96 hours. For areas of interest #2...no tropical cyclone formation shown. For area of interest #3...possible tropical cyclone formation shown by 24 hours near 10N-40W...weakens to a tropical wave near 47W longitude in 96 hours. Elsewhere...has large broad tropical wave emerge from western Africa in 72 hours...shwon to organize into large and organized tropical low pressure spin near 12N-46W in 168 hours.


0600Z GFS Model Run...For area of interest #1...surface low pressure shown forming near 26N-90W in 42 hours...makes landfall on the Texas coast in 84 hours as a surface trough. For area of interest #2...no tropical cyclone formation shown. For area of interest #3...possible compact tropical cyclone shown near 10N-45W in 42 hours...weakens to a tropical wave while moving into the southern Lesser Antilles in 108 hours.


0600Z NAVGEM Model Run...For area of interest #1...shows surface low forming near 26N-92W in 48 hours...making landfall on the Texas coast in 84 hours as a surface trough. For area of interest #2...no tropical cyclone formation shown. For area of interest #3...shows surface low weakening to a tropical wave near 43W longitude in 18 hours. Elsewhere...the current large tropical wave emerging from western Africa is shown to become better organized into a tropical low pressure near 11.5N-30W in 48 hours. Tropical wave currently near 55W longitude shown to organize into a tropical low pressure when it reaches the southern Caribbean Sea in 102 hours...moves into Nicaragua in 126 hours...becomes tropical cyclone on the northwest coast of Honduras in 144 hours (upper-level winds that enhance this tropical wave appear to be from the eastern divergence zone of a westward moving fracture of the current west Atlantic upper vorticity...which after day 5 lifts northward toward western Cuba and allows a supporting upper ridge to build over the southern Caribbean in its wake).

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