*******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.**********
...SUNDAY AUGUST 23 2020 8:30 PM EDT...
See tropical storm Laura and Hurricane 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...While crossing over Haiti and the Dominican Republic over the last day...Laura has remained impressive while continuing to produce a large and circular thunderstorm complex in its circulation. This has prevented much weakening despite the land interaction...and now Laura is stronger than ever (now at 60 mph maximum sustained winds) and becoming better organized while moving into eastern Cuba tonight. My track forecast is unchanged from my previous discussion due to its accuracy...and shows the current west-northwest angle in track continuing around the forecast countour of the southwestern side of the Atlantic subtropical ridge...which has and will continue to build increasigly westward toward the southeasern United States (see Tropical Storm Marco section below for more details on the expected evolution of the surface subtropical ridge). This track will take Laura across Cuba and then the southeastern Gulf of Mexico. What Laura does as it enters the Gulf of Mexico heavily depends on what Hurricane Marco does. Since its likely by 72 hours that Marco will be making its way northwestward inland into the southern Louisiana region...I forecast Laura by 72+ hours to bend more northward in track while gravitated toward the low pressure field of Marco...which very unfortunately means the southern Louisiana region will likely also deal with a Laura landfall not long after Marco. After landfall...I forecast a curve to the north and then northeast toward Arkansas and southeast Missouri as the cut-off upper trough currently over the eastern United States and northwestern Gulf of Mexico will maintain a southwest-to-northeast elongation...with the southwesterly upper flow on the east side of the upper trough helping to guide Laura as Laura is expected to be a strong/tall tropical cyclone by landfall time.
Regarding strength...there does not appear to good news here either as Laura is 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 during much of the forecast period. Although the 24 hour forecast point places Laura over central Cuba...the forecast point is uncomfortably close to the south coast of Cuba...and combined with the organization of the tropical storm I now forecast Laura to already become a hurricane by 24 hours. With Marco remaining a small and sheared tropical cyclone...I do not expect Marco to negatively affect Laura as much at this point...so I now forecast Laura to become a major (category 3+) hurricane as it moves across the Gulf of Mexico. 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 (1800Z Aug 23)...60 mph maximum sustained wind tropical storm centered between northwest Haiti and Cuba at 19.5N-75.2W
IOH 24 Hr Forecast (1800Z Aug 24)...75 mph maximum sustained wind hurricane centered over central Cuba at 21.7N-80.5W
IOH 48 Hr Forecast (1800Z Aug 25)...100 mph maximum sustained wind tropical storm centered in the eastern Gulf of Mexico at 25N-85.2W
IOH 72 Hr Forecast (1800Z Aug 26)...115 mph maximum sustained wind major hurricane centered in the Gulf of Mexico south of Louisiana at 27.7N-91.5W
IOH 96 Hr Forecast (1800Z Aug 27)...105 mph maximum sustained wind hurricane centered just inland and over southwestern Louisiana/southeast Texas border at 30.8N-94W
IOH 120 Hr Forecast (1800Z Aug 28)...40 mph maximum sustained wind tropical storm centered over the eastern Missouri/Arkansas border at 36N-92.2W
HURRICANE MARCO...While continuing northwestward across the Gulf of Mexico under the combined influences of the cut-off upper trough to the west and southeastern United States surface ridge building to the north...Marco is closing in on southern Louisiana and surrounding areas where preparations should be rushed to completed tonight. Although Marco has finally become a minimal category 1 hurricane...it has struggled to do so as the cut-off upper trough has been shearing this system.
Going forward...Marco will be heavily influenced by the cut-off upper trough...as well as the evolution of the western North America upper ridge and also the west Atlantic upper ridges surrounding the upper trough. The cut-off upper trough is expected to gradually weaken while starved of higher latitude colder air...with the Atlantic surface subtropical ridge building westward into the southeastern United States due to reduced upper divergence on the east side of the weakening upper trough and also due to the southeastern convergence zone of the western Atlantic upper ridge. The surface ridging over the southeastern United States will strengthen further as frontal systems over southern Canada driven by shortwave upper troughs will waft the warm air associated with the western North America upper ridge toward the Great Lakes region...with the southeastern convergence zone of the Great Lakes nose of the upper ridge responsbile for strengthening the southeastern United States surface ridge. The Great Lakes nose of the upper ridge is also helping push the cut-off upper trough westward out of the Gulf of Mexico and into the south-central United States.
With the outlook mentioned in the previous paragraph...I expect Marco to continue northwestward in the short term...a combination of the west push of the surface ridge building toward the southeastern United States and north pull of the cut-off upper trough. I have again nudged the forecast track points northeastward due to Marco's track still being more north and less west than previously thought. As Marco nears southern Louisiana...I expect some west bend in track as Marco runs into the strengthening southeastern United states surface ridge...and also as the cut-off upper trough responsible for dragging Marco northward gets pushed westward to the point it has less influence on Marco's track. My track forecast is bent back northward again by 72 hours as Marco rounds the west side of the steering southeastern United States surface ridge...and also catches up to the upper trough which may attepmt to drag Marco northward again. Regarding intensity...I have lowered my intensity forecast as the 1200Z GFS showed more southwesterly shearing winds for the next 24 hours from the cut-off upper trough than it previously showed...and because Marco is slightly weaker than my previous forecast. Marco may also experience shear as Laura as a much larger system than Marco at this point...with the outflow of Laura perhaps enhancing the upper southwesterly wind speed over Marco. However I do forecast Marco to slightly strengthen before its southern Louisiana landfall as I think there is a window where wind shear could drop as the cut-off upper trough continues shifting westward and away...and prior to the arrival of Laura's outflow. See bulletins at the home page of this site for an update on Marco's impact potential given this current outlook.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Aug 23)...75 mph maximum sustained wind hurricane centered over the central Gulf of Mexico at 25.8N-87.8W
IOH 24 Hr Forecast (1800Z Aug 24)...80 mph maximum sustained wind hurricane centered just south of southeastern Louisiana at 28.7N-90.7W
IOH 48 Hr Forecast (1800Z Aug 25)...50 mph maximum sustained wind tropical storm centered just inland and over southwestern Louisiana at 30.7N-93.8W
IOH 72 Hr Forecast (1800Z Aug 26)...Remnant low pressure centered over northeast Texas at 33.2N-95.7W
AREA OF INTEREST #1...A tropical wave of low pressure over western Africa is nearing the west African coast and eastern tropical Atlantic...but has less thunderstorm activity than it did last evening perhaps from the effects of 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 10% 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 southeastward toward the Atlantic tropics in the middle of the forecast period (as the current west Atlantic upper ridge expands into the north Atlantic due to warm air advection ahead of a variety of fronts to emerge from Canada...with the expanded ridge 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 forecast north Atlantic upper ridging.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Aug 24)...0% chance of tropical cyclone formation (just offshore of western Africa near 15N-20W)
IOH 48 Hr Outlook (1800Z Aug 25)...5% chance of tropical cyclone formation (southwestern Republic of Cabo Verde Islands near 15N-25W)
IOH 72 Hr Outlook (1800Z Aug 26)...10% chance of tropical cyclone formation (tropical Atlantic near 15N-30W)
IOH 96 Hr Outlook (1800Z Aug 27)...10% chance of tropical cyclone formation (tropical Atlantic near 15N-35W)
IOH 120 Hr Outlook (1800Z Aug 27)...10% chance of tropical cyclone formation (tropical Atlantic near 15N-40W)
...COMPUTER MODEL SUMMARY...
Not included in this birdseye view post to avoid further delays in releasing this product. Plan to resume this summary in tomorrow's birdseye view post.