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 #71

Updated: Jul 26

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


...SATURDAY JULY 25 2020 5:32 PM EDT...

See Tropical Depression Gonzalo and Hurricane Hanna sections below for all active tropical cyclones being monitored in the Atlantic basin. See area of interest sections below for additional areas being monitored for tropical cyclone formation.


TROPICAL DEPRESSION GONZALO (RECENTLY DOWNGRADED TO REMNANT TROPICAL WAVE)...Dry saharan air pushed southward toward Gonzalo by a large tropical wave axis to the east..at 48W longitude...has caused Gonzalo to weaken to a tropical wave of low pressure that has crossed the southern Lesser Antilles...Trinidad and Tobago...and northeastern Venezuela...now entering the southeastern Caribbean Sea. None of today's computer model runs regenerate Gonzalo as its remnant wave moves across the Caribbean...and this could be due to the fact the brisk moving wave will quickly arrive directly beneath upper vorticity that stretches across the central Caribbean from the western Atlantic...an environment which will lack upper divergence needed for thunderstorms. Ignoring the NAVGEM model run which keeps Gonzalo as a tropical cyclone that moves across the Caribbean...because its initialization shows Gonzalo way too strong to begin with. This is my final statement on Gonzalo as it is no longer a tropical cyclone.


HURRICANE HANNA...Hanna has strengthened into an impressive category 1 hurricane this morning and through this afternoon while the eye approaches landfall on the Texas coast between Corpus Christi and Brownsville. Conditions for strengthening include an upper ridge expanding from the southern United States that continues to entirely cover Hanna with low shear and upper anticyclonic outflow...and the rather warm 30 deg C Gulf of Mexico waters. Although a cool core shortwave upper trough fragment has been amplifying southward toward Hanna due to the amplification of the upper ridge over southern United States...it appears Hanna's tremendous thunderstorm latent heat release has and will continue to keep this cool core feature pushed away such that it will not disrupt the storm. Hanna has been moving at a more southward angle than previously thought as the hurricane has become strong/tall enough to get dragged by upper northerly winds on the southeast side of the southern United States upper ridge and west side of the aforementioned shortwave upper trough feature...therefore my updated forecast track points are adjusted south and west due to the current position and heading of Hanna.


Various model runs like to keep Hanna's strength for some time after this afternoon's landfall. I think this maybe a suggestion by the models that there could be an area of supportive split flow upper divergence between the southwest side of the approaching shortwave upper trough fragment and south side of the amplifying southern US upper ridge. Therefore on the home page of this site...I mention some impacts over inland southern Texas...spreading into northern Tamaulipas...northern Nuevo Leon and much of the Coahuila provinces of Mexico (previously I only mentioned the eastern part of Coahuila...but given that the shortwave upper trough will now likely stay northeast of Hanna instead of coming directly overhead and suppressing it quickly...I think now much of Coahuila could see heavy rainfall from Hanna).

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

0 Hr Position (1800Z Jul 25)...85 mph maximum sustained wind hurricane centered just southeast of Matagorda Bay Texas at 26.8N-97W

IOH 24 Hr Forecast (1800Z Jul 26)...45 mph maximum sustained wind tropical storm centered over northeastern Mexico at 26N-100W

IOH 48 Hr Forecast (1800Z Jul 27)...Remnant low pressure over central Mexico centered at 25N-103W


AREA OF INTEREST #1...The south side of the large tropical wave of low pressure in th eeastern tropical Atlantic has continued to produce multiple organized thunderstorm bands...as a result it appears pressures have dropped further south and a center of low pressure appears to be forming near 11N-31W. Computer models seem to be picking up on this development...with now all of the models agreeing on developing this tropical wave into a tropical cyclone over the next five days. As a results I have significantly raised my odds of tropical cyclone formation to 80%. However I only gradually raise odds of development to the 80% over the next five days to give time for the large circulation to consolidate and also mix out any dry saharan air that may intrude from the north. During the forecast period...the tropical wave will remain in favorable low shear and upper outflow beneath a broad tropical upper ridge in the region and over warm waters. A more northward angle in track is shown by 120 hours as the tropical wave will likely be a strengthening tropical cyclone by that timeframe...tall enough to be dragged by the southeasterly upper flow on the southeast side of an axis of upper vorticity to persist from the central to western Atlantic. Interests in the northern Lesser Antilles are urged to monitor the progress of this tropical wave over the next few days.

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

IOH 24 Hr Outlook (1800Z Jul 26)...40% chance of tropical cyclone formation (tropical Atlantic near 11.5N-37W)

IOH 48 Hr Outlook (1800Z Jul 27)...50% chance of tropical cyclone formation (tropical Atlanic near 12N-43W)

IOH 72 Hr Outlook (1800Z Jul 28)...60% chance of tropical cyclone formation (tropical Atlanic near 12.5N-49W)

IOH 96 Hr Outlook (1800Z Jul 29)...70% chance of tropical cyclone formation (tropical Atlantic east of the Lesser Antilles near 13N-55W)

IOH 120 Hr Outlook (1800Z Jul 30)...80% chance of tropical cyclone formation (just east of the northern Lesser Antilles near 16N-60W)


AREA OF INTEREST #2...The north end of a tropical wave of low pressure has continued to organize into an active surface trough of low pressure while passing the waters north of the Dominican Republic and now heading into the northwestern Bahamas. This disturbance continues to be supported by upper divergence on the east side of upper vorticity in the western Atlantic...and based on its organization I have introduced it as an area of interest for tropical development due despite no computer model support showing development. This is due to the fact it apperas this disturbance will turn northwestard and northward while rounding the west side of the Atlantic surface subtropical ridge...then accelerate northeastward into the open western Atlantic in strong surface flow to form between the subtropical ridge and an approaching frontal system from the north-central United States. This path will curve the disturbance along warm Gulf stream waters and beneath northwestern Atlantic upper ridging which will keep wind shear low and upper outflow favorably high. I have odds of tropical cyclone formation at a low peak of 30% for the next five days until computer model support comes onboard...or unless the National Hurricane Center begins to mention this disturbance in their tropical weather outlook.

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

IOH 24 Hr Outlook (1800Z Jul 26)...20% chance of tropical cyclone formation (just north of the western Bahamas near 27N-77.5W)

IOH 48 Hr Outlook (1800Z Jul 27)...30% chance of tropical cyclone formation (just offshore of northeastern Florida near 30N-80W)

IOH 72 Hr Outlook (1800Z Jul 28)...30% chance of tropical cyclone formation (just offshore of the Carolinas near 32.5N-77W)

IOH 96 Hr Outlook (1800Z Jul 29)...30% chance of tropical cyclone formation (western Atlantic near 35N-71W)

IOH 120 Hr Outlook (1800Z Jul 30)...30% chance of tropical cyclone formation (northwestern Atlantic near 37.5N-63W)


...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 Tropical Storm Gonzalo...dissipates into a tropical wave entering the southeast Caribbean Sea in 6 hours. For Hurricane Hanna...continues west-southwestward inland across south Texas and into northeast Mexico where it loses its identity in 36 hours. For area of interest #1...tropical cyclone formation shown in 78 hours near 15N-51W...reaches northern Lesser Antilles as a strong tropical cyclone in 120 hours. For area of interest #2...no tropical cyclone formation shown


1200Z ECMWF Model Run...For Tropical Depression Gonzalo...dissipates into a tropical wave entering the southeast Caribbean Sea over the next 24 hours. For Hurricane Hanna...continues west-southwestward inland across south Texas and into north-central Mexico where it loses its identity just after 48 hours. For area of interest #1...tropical cyclone formation shown near 15N-55W in 96 hours...reaches the northern Lesser Antilles in 120 hours while strengthening further. For area of interest #2...no tropical cyclone formation shown


1200Z GFS Model Run...For Tropical Storm Gonzalo...dissipates into a tropical wave in the southeast Caribbean Sea in 18 hours. For Hurricane Hanna...continues west-southwest into central Mexico where it loses its identity in 72 hours. For area of interest #1...tropical cyclone formation shown in 72 hours near 11.5N-47.5W...reaches northern Lesser Antilles as an intense tropical cyclone in 138 hours. For area of interest #2...no tropical cyclone formation shown


1200Z NAVGEM Model Run...For Tropical Depression Gonzalo...shown to gradually strengthen while moving west-northwest aross the open Caribbean Sea...reaches Yucatan channel between Cuba and the Yucatan peninsula of Mexico in 120 hours as a strong tropical cyclone. For Hurricane Hanna...continues west-southwest into central Mexico where it loses its identity in 72 hours. For area of interest #1...tropical cyclone formation shown near 11.5N-36.5W in 48 hours...becomes an intense tropical cyclone centered near 15N-51W in 120 hours. For area of interest #2...no tropical cyclone formation shown

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