*******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 3 2020 1:27 PM EDT...
See Tropical Storm Isaias section below for the only active tropical cyclones in the Atlantic basin. See area of interest section below for a surface trough of low pressure in the western Atlantic being monitored for development.
TROPICAL STORM ISAIAS...Isaias continues northward in track along 80W longitude while guided by deep-layered southerly flow ahead of an approaching upper trough and surface cold front from the eastern United States. The incoming upper trough has become more amplified while being injected with cooler air from a higher-latitude Canadian upper trough phasing with it...thus the upper wind flow ahead of the upper trough has become increasingly southerly and more aligned with the forward motion of the storm...thus reducing the shear that has been negatively affecting Isaias. In response on visible satellite...Isaias appears to be becoming slowly better organized while the thickest thunderstorm bands once sheared east of the center have been able to wrap into the north side of the circulation. Colorized infrared on the other hand shows Isaias is still struggling with a lack of activity on the south side of the center...a sign of some southerly shear from the upper trough. Thus it is possible Isaias may become a hurricane before moving into the eastern Carolinas tonight....or maybe it will not from the shear.
Even though Isaias is slightly south of my previous forecast...I have made no changes as the models agree that Isaias will be slingshotted quickly by the upper trough into New Jersey by 24 hours. Regarding intensity...I am continuing my previous forecast where Isaias is at 70 mph maximum sustained winds for much of its remaining life cycle. Even though the circulation will be interacting with land from the Carolinas to the northeastern United States...I keep this intensity through 24 hours as Isaias will remain supported by divergence on the east side of the incoming upper trough...and the east side of the circulation will likely remain over 26+ deg C waters that extend all the way unusually far north to the New Jersey coast...thus I do not think it will lose tropical characteristics before 24 hours...espeically as the cold front being driven by the upper trough will still be off to the west. I continue to show a lower intensity at the end of the forecast period (48 hours) as models still show the more amplified upper trough generating a seperate frontal low pressure center west of Isaias that will be the dominant non-tropical feature in the region (a few days ago it looked like from the models Isaias was supposed to transition to the dominant non-tropical feature). Thus wind impacts across New Brunswick...Nova Scotia...and Prince Edward Island by Wednesday do not look to be significant. See bulletins at the home page of this site for additional details on the expected impacts of Isaias.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Aug 3)...70 mph maximum sustained wind tropical storm centered offshore of the Florida/Georgia border at 30.7N-80.1W
IOH 24 Hr Forecast (1200Z Aug 4)...70 mph maximum sustained wind tropical storm centered just offshore of southern New Jersey and Delaware at 39N-74.8W
IOH 48 Hr Forecast (1200Z Aug 5)...Remnant frontal low centered over New Brunswick just east of the Maine border at 46.5N-67W
AREA OF INTEREST #1...The surface trough of low pressure passing north of the Lesser Antilles and Caribbean Islands is producing thunderstorm activity with the help of upper outflow from a warm western Atlantic upper ridge overspreading the region...and is currenlty located in the vicnity of 22N-65W. Due to the continued withdrawing computer model support and reduced organization of the disturbance (as the spin has been less defined than it was yesaterday)...I have dropped my peak odds of development to 50%. By 48+ hours...I slowly drop the odds of development downward as the upper trough forecast to recurve Tropical Storm Isaias north and northeast merges with the nearby upper vortex to the west...and also pushes the vortex pushed toward the disturbance...which will likely begin to increase some wind shear. Forecast track of this disturbance is initially straightfoward...a west-northwest to northwest trajectory around the southwest side of the Atlantic surface subtropical ridge. The forecast track keeps this system away from land areas...passing between the Caribbean Islands and Bermuda...and offshore of the eastern United States. The forecast track becomes a little murky by 96+ hours as the upper trough that recurves Isaias passes to the north...with its western convergence zone producing another surface ridge over the Great Lakes region of North America potentially stalling the northwest track of this disturbance. I have shifted my forecast points around this timeframe more southwestward as the 1200Z GFS shows this surface ridge bridging with the Atlantic subtropical ridge...which will provide an opportunity for some westward drifting. However Isaias will leave behind a trailing cold front that will be sandwiched between the ridges...and I show the disturbance drifting north toward the trailing front as it approaches in 120 hours. I drop odds of development to near 0% by this timeframe as the front will have potential to absorb this disturbance...and the more north position of the disturbance will expose it to mid-latitude upper westerlies that will increase the unfavorable shear further.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Aug 4)...50% chance of tropical cyclone formation (western Atlatnic near 25N-70W)
IOH 48 Hr Outlook (1200Z Aug 5)...35% chance of tropical cyclone formation (western Atlantic near near 31N-72W)
IOH 72 Hr Outlook (1200Z Aug 6)...20% chance of tropical cyclone formation (western Atlantic near 33N-72W)
IOH 96 Hr Outlook (1200Z Aug 7)... 20% chance of tropical cyclone formation (east of North Carolina near 33N-74W)
IOH 120 Hr Outlook (1200Z Aug 8)...5% chance of tropical cyclone formation (east of North Carolina near 36N-74W)
...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 Isaias...shown to make landfall on the northeastern South Carolina coast in 30 hours...moves across the eastern Carolinas and southeast Virginia through 36 hours...moves across eastern Maryland & Delaware & New Jersey by 48 hours...moves across Vermont and New Hampshire in 54 hours...while moving across Maine and New Brunswick in 66 hours quickly weakens and loses its identity to frontal low pressure to the west. For area of interest #1...no tropical cyclone formation shown.
0000Z ECMWF Model Run...For Tropical Storm Isaias...makes landfall in northeastern South Carolina just after 24 hours...moves rapidly north-northeast and reaches New Jersey by 48 hours...weakens considerably by 72 hours while over the south Quebec coast as frontal low pressure to the northwest dominates. For area of interest #1...no tropical cyclone formation shown
1200Z GFS Model Run...For Tropical Storm Isaias...makes landfall in southeastern South Carolina in 18 hours...moves across eastern North Carolina and southeast Virginia through 24 hours...reaches southwestern New Jersey in 30 hours...centered over Vermont in 36 hours...loses identity just north of the Maine Border in New Brunswick in 48 hours to a frontal low pressure forming to the west. For area of interest #1...no tropical cyclone formation shown.
0600Z NAVGEM Model Run...For Tropical Storm Isaias...makes landfall over the North Carolina/South Carolina border in 24 hours...reaches waters just offshore of New Jersey in 42 hours...over Cape Cod Massachusetts in 54 hours...moves into New Brunswick and Nova Scotia in 66 hours while still at high strength...weakens over Newfoundland in 84 hours...located over the north Atlantic as a remnant frontal low at 55N-47.5W in 120 hours. For area of interest #1...no tropical cyclone formation shown