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 #102

*******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 AUGUST 25 2020 2:57 PM EDT...

See Hurricane Laura section below for the only currently active tropical cyclone in the Atlantic basin. See area of interest section below for an eastern Atlantic tropical wave of low pressure being monitored for tropical cyclone formation. Elsewhere...another tropical wave of low pressure over western Africa is producing a large area of thunderstorms with some signs of organization. Some of the long range computer model runs (120+ hours) suggest this tropical wave could slowly develop as it moves across the Atlantic tropics...possibly merging with the current wave in the eastern Atlantic as it does so. If this tropical wave continues to be active as it moves toward the west coast of Africa in the next 24 hours...I will be introducing it as another area of interest for tropical development.


HURRICANE LAURA...Laura has continued to slowly organize while clearing western Cuba and entering the southeastern and southern Gulf of Mexico...finally strengthening into a minimal category 1 hurricane as of this morning. Although Laura has been tracking more west and less north during its slow intensification process...recently satellite animation suggests a jog with a bigger northward angle perhaps while the outer circulation of Laura begins to absorb the fading remnant low pressure of what was Tropical Storm Marco. Therefore my updated forecast track continues to have the landfall point at the Texas/Louisiana border...but with a slightly sooner landfall just before 48 hours with the assumption the recent increase in the northward angle in track continues. The northwestward track thru landfall time is not only being induced by the low pressure field of Marco's remnant...but also as Laura rounds the west side of the southeastern United States surface ridge and also as the strong/tall hurricane feels the influence of the upper southwesterly flow out ahead of a cut-off upper trough over the central United States. After landfall...the central United States upper trough will be pushed eastward by another upper trough incoming from western Canada...which should quickly curve Laura more eastward in track toward the Kentucky/southern Ohio valley/Appalachian mountain region as it transitions into a remnant low supported by the eastern divergence zone of the eastward-shifting upper trough. It is interesting to note that the 0000Z CMC and 1200Z GFS dissipate Laura's remnant low before it gets to the Ohio Valley/Appalachian region...perhaps as those runs see the remnant low getting caught beneath the western convergent size of the upper trough from western Canada...while the 0000Z ECMWF shows the remnant low holing onto some vigor and then strengthening in the western Atlantic offshore of the eastern United States as a frontal cyclone while it shows Laura's remnant low aligning with the supportive eastern divergence zone of the upper trough. Thus there is some uncertainty as to exactly which side of the upper trough Laura's remnant will engage with...thus long term uncertainty as to the fate of the remnants.


Regarding strength...Laura up until landfall with the Texas/Louisiana border region will remain underneath an expansive western Atlantic upper ridge with a vast area of low shear and upper outflow...and will also be passing over very warm waters. However I have lowered my intensity forecast as Laura is still taking time to develop an organized inner core...with last night's infrared satellite and today's visible satellite showing Laura only slowly developing an eye wall while it tries to wrap the thunderstorm bands on its south side around its center. However my intensity forecast assumes Laura will still become a major category 3 hurricane just before landfall (perhaps as high as 120 mph maximum sustained winds just before 48 hours...then weakening to 115 mph at 48 hours just after landfall time). Even if Laura comes in as a category 1 or 2 hurricane...there will be dangerous coastal storm surge flooding...damaging winds...and heavy flash flooding rains in and around the landfall region. See bulletins at the home page of this site for an update on Laura's impact potential given this current outlook.

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

0 Hr Position (1200Z Aug 25)...75 mph maximum sustained wind hurricane centered in the southeastern Gulf of Mexico at 23.7N-87W

IOH 24 Hr Forecast (1200Z Aug 26)...105 mph maximum sustained wind hurricane centered in the Gulf of Mexico south of Louisiana at 27.5N-91.5W

IOH 48 Hr Forecast (1200Z Aug 27)...115 mph maximum sustained wind major hurricane centered just inland and over the Texas/Lousiana border at 30.5N-94W

IOH 72 Hr Forecast (1200Z Aug 28)...35 mph maximum sustained wind tropical depression centered over northeastern Arkansas at 35.5N-91.2W

IOI 96 Hr Forecast (1200Z Aug 29)...Remnant low pressure centered over Kentucky/West Virginia border at 37.5N-82.5W


REMNANTS OF MARCO...Southwesterly shearing upper level winds being generated between an upper ridge to the east and central United States cut-off upper trough to the west have weakened Tropical Storm Marco further to a remnant low pressure drifting westward just offshore of the south-facing Louisiana coast under the steering influence of the surface ridge over the southeastern United States. The moisture from this system remains sheared off well to the northeast and is producing showers and thunderstorms stretched across the southeastern United States (currently over southern Mississippi...northern Alabama..northern Georgia...and reaching into the western Carolinas). The remnant low pressure of Marco is expected to soon lose its identity to the outer low pressure field of Hurricane Laura closing in from the southeast...therefore impacts from this remnant tropical system are not expected to spread elsewhere. This is my final statement on Marco on this blog as it is no longer a tropical cyclone.


AREA OF INTEREST #1...A tropical wave of low pressure in the eastern tropical Atlantic continues producing thunderstorm bands on its south side...while the north side remains suppressed by dry saharan air. Outside of the dry air...conditions in the eastern tropical Atlantic will be favorable for this tropical wave to develop as a tropical upper ridge axis with low shear and upper outflow will prevail in the region. However my peak 5-day odds of tropical cyclone formation are only 15% at the present time as dry saharan air has recently had a history of hampering development in the eastern tropical Atlantic. The 1200Z GFS shows some of the current northeast Atlantic upper vorticity getting pushed south toward the Atlantic tropics in the middle of the forecast period...as the current west Atlantic upper ridge expands into the northeast Atlantic due to warm air advection ahead of a vigorous frontal cyclone to emerge from eastern Canada...with the expanded upper ridging pushing on the upper vorticity. However I do not expect this upper vorticity to negatively affect this tropical wave's development as the upper vorticity is then shown to retrograde westward and away around the expanded upper ridging. The 1200Z GFS also showed the strong tropical wave currently producing widespread thunderstorms over western Africa slowly merging with this wave through 120 hours as both waves move into the central tropical Atlantic...which is another reason I keep odds of development on the low side as it is unclear if the merged system will be a continuity of this wave or the other tropical wave.

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

IOH 24 Hr Outlook (1200Z Aug 26)...0% chance of tropical cyclone formation (tropical Atlantic near 10.5N-29W)

IOH 48 Hr Outlook (1200Z Aug 27)...15% chance of tropical cyclone formation (tropical Atlantic near 11N-34W)

IOH 72 Hr Outlook (1200Z Aug 27)...15% chance of tropical cyclone formation (tropical Atlantic near 11.5N-39W)

IOH 96 Hr Outlook (1200Z Aug 28)...15% chance of tropical cyclone formation (tropical Atlantic near 12N-44W)

IOH 120 Hr Oulook (1200Z Aug 29)...15% chance of tropical cyclone formation (tropical Atlantic near 12.5N-49W)


...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 Hurricane Laura...makes landfall in southeastern Texas between the Texas/Louisiana border and Houston in 54 hours...rapidly weakens to a remnant low pressure over northwestern Arkansas which dissipates by 90 hours. For area of interest #1...no tropical cyclone formatio shown.


0000Z ECMWF Model Run...For Hurricane Laura...makes landfall as an intense hurricane over Houston Texas just after 48 hours...slowly weakens while located inland over the northeast Texas/Arkansas border in 72 hours...remnant low pressure only gradually weakens while accelerating eastward into western Virginia by 120 hours. For area of interest #1...no tropical cyclone formation shown.


1200Z GFS Model Run...For Hurricane Laura...makes landfall as an intense hurricane just west of the Texas/Louisiana border in 42 hours...remnant low pressure locaed over the Missouri/Arkansas/Texas/Kentucky border region in 84 hours an loses its identity shortly thereafer. For area of interest #1...no tropical cyclone formation shown.


0600Z NAVGEM Model Run... For Hurricane Laura...makes landfall over Matagorda Bay Texas in 54 hours as an intense hurricane...remnant low pressure slowly weakens and located over west-central Arkanas in 126 hours. For Tropical Storm Marco...gradually loses its idenity just south of Louisiana just after 24 hours as Laura to the southeast becomes the dominant low pressure system in the Gulf of Mexico. For area of interest #1...no tropical cyclone formation shown.

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