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 #101

*******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 24 2020 11:22 AM EDT...

See tropical storm Laura and tropical storm Marco sections below for the two currently active tropical cyclones in the Atlantic basin. See area of interest section below for tropical wave of low pressure being monitored for tropical cyclone formation.


TROPICAL STORM LAURA...Instead of passing directly over Cuba...the center of Tropical Storm Laura has managed to stay over warm northwestern Caribbean Sea waters just south of Cuba. I think this is due to the fact Laura has been underneath the south side of an expansive western Atlantic upper ridge axis instead of directly below it...thus some northerly flow from the upper ridge axis maybe keeping Laura pushed a bit southward. The northerly push from the upper ridge axis has been evident by lessened thunderstorm activity and upper outflow on the north side of Laura...while the outflow and thunderstorm activity on the south side of Laura has been vibrant. It is possible that the latent heat release of the stronger southern thunderstorm bands and their resulting warm core upper outflow have dropped surface pressures further south such that the center of Laura has trended further south. With the center over water instead of land...Tropical Storm Laura has been able to intensify further to 65 mph maximum sustained winds.


My track forecast is nudged southward and now brings the center of Laura into the Texas/Louisiana border by 72 hours after it crosses central and western Cuba and the Gulf of Mexico. There is remarkable agreement between the 0000Z ECMWF...0600Z GFS...and 0000Z NAVGEM with this track. In addition to the more southward initial position of Laura...it makes sense to nudge the forecast points southward as Marco has weakened sooner than I anticipated...thus its low pressure field will have less of a northward pull on Laura. What will make Laura eventually turn more northward for a landfall is that it will reach the west extent of the southeastern United States nose of the Atlantic surface subtropical ridge...and also Laura will likely be strong/tall enough to be turned northward by the southwesterly flow on the east side of the central United States cut-off upper trough...forecast to be generally stationary through most of the forecast period while jammed between the western North America upper ridge and western Atlantic upper ridge. After landfall...this upper trough will finally be pushed eastward by another upper trough incoming from western Canada...which should quickly curve Laura more eastawrd in track toward the Kentucky/Ohio valley region as it transitions into a remnant low supported by the eastern divergence zone of the eastward-shifting upper trough.


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. I have lowered my intensity forecast in the short-term as Laura is not quiet yet a hurricane while lacking a tight core of thunderstorms...perhaps as it recovers from land interaction. However my forecast assumes that Laura will soon develop such a core and rapidly intensify into a major hurricane (at least category 3). I have slightly raised my peak intensity in the forecast comapred to my previous as the more southward adjusted track gives a little more time for Laura to stay over the Gulf of Mexico waters before landfall. 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 24)...65 mph maximum sustained wind tropical storm centered just south of central Cuba at 20.9N-79.7W

IOH 24 Hr Forecast (1200Z Aug 25)...90 mph maximum sustained wind hurricane centered in the eastern Gulf of Mexico at 24N-85W

IOH 48 Hr Forecast (1200Z Aug 26)...115 mph maximum sustained wind major hurricane centered in the Gulf of Mexico south of Louisiana at 26.5N-91W

IOH 72 Hr Forecast (1200Z Aug 27)...125 mph maximum sustained wind major hurricane making landfall at the Texas/Louisiana border at 29.8N-94W

IOH 96 Hr Forecast (1200Z Aug 28)...40 mph maximum sustained wind tropical storm centered over eastern Arkansas at 35N-92W

IOI 120 Hr Forecast (1200Z Aug 29)...Remnant low pressure centered over eastern Kentucky at 37.5N-83W


TROPICAL STORM MARCO...Overnight...Marco surprised us by tracking further east under the influence of 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. This has increased the rainfall flooding...gusty wind...and coastal sea swell potential for this morning and afternoon at locations further east...from the western Florida panhandle to southeastern Louisiana. Marco has continued to weaken to a moderate to weak tropical storm this morning as the southwesterly shear has seperated the heaviest thunderstorm clouds from the surface low pressure swirl of the storm...and visible satellite imagery suggests the swirl is beginning to turn more westawrd toward the south Louisiana coast. Therefore my updated forecast track shown below has Marco drifitng westawrd along the coastline while the shear weakens it to a remnant low pressure. There is a possiblity that the remnant low pressure of Marco produces rainfall also over southwestern Louisiana or maybe even southeast Texas if it is able to fire thunderstorm bursts later on...with the possiblity of such bursts being induced by the eastern divergence zone of the central United States cut-off upper trough.

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

0 Hr Position (1200Z Aug 24)...50 mph maximum sustained wind tropical storm centered just southeast of southeastern Louisiana at 28.1N-88.4W

IOH 24 Hr Forecast (1200Z Aug 25)...Remnant low pressure centered over the south-central Louisiana coast at 30N-91.5W


AREA OF INTEREST #1...A tropical wave of low pressure exiting the west coast of Africa and entering the eastern tropical Atlantic is producing increased 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...but these odds are slightly higher than in my previous outlook for this system yesterday given the increased thunderstorm bands. The outlook positions are also adjusted southward toward the currently more active portion of the tropical wave. The 0600Z 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.

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

IOH 24 Hr Outlook (1200Z Aug 25)...0% chance of tropical cyclone formation (southwestern Republic of Cabo Verde Islands near 10N-24W)

IOH 48 Hr Outlook (1200Z Aug 26)...10% chance of tropical cyclone formation (tropical Atlantic near 10.5N-29W)

IOH 72 Hr Outlook (1200Z Aug 27)...15% chance of tropical cyclone formation (tropical Atlantic near 11N-34W)

IOH 96 Hr Outlook (1200Z Aug 27)...15% chance of tropical cyclone formation (tropical Atlantic near 11.5N-39W)

IOH 120 Hr Outlook (1200Z Aug 28)...15% chance of tropical cyclone formation (tropical Atlantic near 12N-44W)


...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 Tropical Storm Laura...no strengthening shown till 30 hours when Laura enters Gulf of Mexico from Cuba...makes landfall in south-central Louisiana as a strong tropical cyclone in 72 hours. For Tropical Storm Marco...gradually loses its idenity just south of Louisiana by 36 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 formatio shown


0000Z ECMWF Model Run...For Tropical Storm Laura...rapid strengthening shown along northwest Cuba coast in 24 hours...makes landfall as an intense tropical cyclone over the Texas/Louisiana border in 72 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. Elsewhere...tropical wave emerges from western Africa in 72 hours...organizes into a tropical low pressure near 16.5N-32.5W in 120 hours.


0600Z GFS Model Run...For Tropical Storm Laura...rapid strengthening shown along northwest Cuba coast in 24 hours...makes landfall as an intense tropical cyclone over the Texas/Louisiana border in 72 hours. For Tropical Storm Marco...while weakening shown to make landfall over southeastern Louisiana in 18 hours...dissipates over south-central Louisiana in 30 hours. For area of interest #1...no tropical cyclone formation shown.


0600Z NAVGEM Model Run... For Tropical Storm Laura...no strengthening shown till 30 hours when Laura enters Gulf of Mexico from Cuba...makes landfall over over the Texas/Louisiana border in 72 hours as a strong tropical cyclone. 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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