Since 2012 on the Weather Underground ( 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 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 

  • NCHurricane2009


*******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 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 dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********

...WEDNESDAY AUGUST 5 2020 1:01 PM EDT...

See remnants of Isaias section below for a final statement on this weather system. See area of interest section below for a mid-level trough of low pressure in the western Atlantic being monitored for development.

REMNANTS OF ISAIAS...Tropical Storm Isaias has been declared non-tropical over the last 24 hours while the center of circulation continued north-northeast across eastern New York State...then northern Vermont...and then southeastern Quebec. The remnant low is now frontal in nature while the cold front of the upper trough it is interacting with has overspread the circulation...and the remnant low remains supported by the eastern divergence zone of the upper trough. The eastern divergence zone of the upper trough is also triggering surface pressure falls to the west of the remnant low in the vicinity of the Quebec/Ontario border. The CMC model is the only model run that insists the western lobe of low pressure will become the dominant while Isaias loses its identity...while the GFS...ECMWF...and NAVGEM have switched to Isaias remaining the dominant frontal low in the region. Regardless of which feature dominates...this weather system is forecast to shift east into the north Atlantic from the Canadian Labrador coast in 48 hours...then pass south of Greenland and approach Iceland in about 4 day as the supporting parent upper trough shifts east. This is my final statement on Isaias on this blog as it is no longer a tropical feature.

AREA OF INTEREST #1...The western Atlantic surface trough of low pressure passing through the western Atlantic between Bermuda and the Caribbean Islands has stalled out in the vicinity of 30N-70W while a surface ridge building over the eastern United States has blocked this system's progress around the Atlantic surface subtropical ridge. This system has not become any better organized while producing only a limited amount of showers and thunderstorms...and as of 1200Z is no longer shown in the NHC TAFB surface analysis map...thus we can assume as of 1200Z this system is now only a mid-level trough of low pressure. This system has become stalled at a location further south than I previously I have shifted my forecast points southward while assuming that this system will begin a slow westward drift as the two surface ridges merge to the north of the disturbance...with the track being slow as the surface cold front trailing from the remnants of be supported by the eastern divergence zone of the south fracture of the eastern North America upper trough...keeps the surface ridging in the vicnity of the disturbance weak. The more south track reduces the chances that the trailing front will absorb this disturbance and exposes the disturbance to less wind shear from the forecast south fracture upper trough...therefore I have extended my outlook below to 120 hours. I dip the odds of development to a minimum of 5% at 72 hours...then slowly raise them back to 10% after that time as the south fracture upper trough and its shearing upper westerly winds move away. The reason I am keeping low 10% odds in the long range despite the forecast reduction in shear is models do not forecast development...and its possible this disturbance dissipates in the shear in the middle of the 120-hour forecast period. By 120 hours...I curve the track of the disturbance northbound as the eastern United States surface ridge becomes eroded by the next upper trough in the mid-latitude westerlies. Even though the forecast track takes this system close to the southeastern United States coast in the long range...not mentioning the potential for impacts on the home page of this site as it is possible the disturbance does not survive.

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

IOH 24 Hr Outlook (1200Z Aug 6)...20% chance of tropical cyclone formation (western Atlantic near 30N-72W)

IOH 48 Hr Outlook (1200Z Aug 7)... 10% chance of tropical cyclone formation (western Atlantic near 30N-74W)

IOH 72 Hr Outlook (1200Z Aug 8)...5% chance of tropical cyclone formation (western Atlantic near 30N-76W)

IOH 96 Hr Outlook (1200Z Aug 9)...10% chance of tropical cyclone formation (offshore of the southeastern United States near 30N-78W)

IOH 120 Hr Outlook (1200Z Aug 10)...10% chance of tropical cyclone formation (just offshore of South Carolina near 32N-78.5W)


Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (

0000Z CMC Model Run...For area of interest tropical cyclone formation shown.

0000Z ECMWF Model Run...For area of interest tropical cyclone formation shown.

0600Z GFS Model Run...For area of interest tropical cyclone formation shown.

0600Z NAVGEM Model Run...For area of interest tropical cyclone formation shown.


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