Since 2012 on the now retired 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 at Yale Climate Connections via Disqus where the former Weather Underground community has moved to. Feel free to reply to me there, at my Disqus feed at this link, or via 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.**********

...SUNDAY NOVEMBER 17 2019 4:55 PM EDT...

See area of interest sections below for areas being monitored for tropical development in the Atlantic basin.

AREA OF INTEREST #1...The thunderstorm squalls and surface trough of low pressure in the central tropical Atlantic remains supported by the eastern divergence zone of an upper trough in the region. Based on the latest ASCAT-A descending appears the location of maximum spin on the surface trough remains unchanged near 16N-54W...which places the surface trough on the west side of the squally weather as the upper trough is also shearing the thunderstorm squalls eastward from the surface trough. Due to the current positon of maximum surface spin...I have nudged my forecast track in the updated outlook below southward. The forecast track continues to show this disturbance curving increasingly northwestward and then northward while rounding the west side of the Atlantic subtropical ridge and east side of the frontal cyclone mentioned in area of interest #2. After this frontal cyclone ejects northward into Atlantic Canada during the early part of the forecast period...the upper trough currently over the central US will have arrived into the western Atlantic and produced another frontal low...which guaruntees this disturbance will continue northward...followed by a northeastward acceleration by 96 hours as the cold front of the second frontal low absorbs this disturbance. The Euro (ECMWF) model continues to suggest tropical cyclone formation from this disturbance...while the NAVGEM and CMC models are showing a stronger surface low pressure form when compared to yesterday's runs. Meanwhile the GFS continues to not show development. I think whether or not this disturbance develops into a tropical cyclone will depend on whether or not this disturbance produces enough thunderstorm latent heat release to defeat the cold core shearing central Atlantic upper trough just to the west...and eastern Atlantic cut-off upper vortex beginning to approach from the northeast while pushed by the expanding upper ridge to the northwest. Given the increase in model support in the NAVGEM and CMC along with the Euro still showing development...and given the increase in thunderstorm intensity in the latest colorized infrared satelilte...I have increased my peaks odds of development to 25%...and show non-zero odds in the 48 to 72 hour timeframe as this is when this disturbance will be moving into the lower shear of the aforementioned upper ridge...but the shear may not be completely absent if the central Atlantic upper trough still lingers by that timeframe and if the southwesterly winds of the absorbing cold front's upper trough impenges too much from the west.

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

IOH 24 Hr Outlook (1200Z Nov 18)...0% chance of tropical cyclone formation (central Atlantic near 19N-57.5W)

IOH 48 Hr Outlook (1200Z Nov 19)...15% chance of tropical cyclone formation (central Atlantic near 23N-61W)

IOH 72 Hr Outlook (1200Z Nov 20)...25% chance of tropical cyclone formation (central Atlantic near 26.5N-61W)

IOH 96 Hr Outlook (1200Z Nov 21)...0% chance of tropical cyclone formation (absorbed by cold front near 31N-55W)

AREA OF INTEREST #2...The strengthening frontal cyclone located just offshore of the southeastern United States is in a classical mature phase...with the cold air advection (southward cold air transport) on the west side of the cyclone amplifying its supporting cold core upper trough...with the upper trough axis beginning to stack over the surface circulation as enough cold air wraps around the surface center. The surface circulation has passed 32N-74.5W earlier this afternoon and is moving notably eastward...and has been firing bands of gusty thunderstorms on its north side since yesterday...some of which reached the Carolina coast...and now currently has small pockets of showers and thunderstorms. Given that the surface circulation over the next 24 hours will be near warm Gulf stream waters and under the cold temperatures of its parent upper trough...will be watching for the development of instability and increased thunderstorms...but I only have the odds of subtropical cyclone formation at 10% given that this cyclone is not being mentioned in the National Hurricane Center tropical weather outlook so far. Between 24 and 48 hours...the parent upper trough and surface cyclone will be swung rapdily northward into Nova Scotia by the larger upper trough currently approaching from the central United States...with cooler water temperatures and land interaction ending potential for tropical development. Regardless...this system will bring sea swells to the eastern United States coast and Atlantic Canada coasts through Tuesday...and by late Monday and Tuesday bring gusty winds and heavy rain from coastal Massachusetts to coastal Maine as well as Nova Scotia and Newfoundland...with some of these areas having a wintry mix of precipitation on the colder west side of the cyclone.

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

IOH 24 Hr Outlook (1200Z Nov 18)...10% chance of subtropical cyclone formation (offshore of the eastern United States near 34N-65W)

IOH 48 Hr Outlook (1200Z Nov 19)...0% chance of subtropical cyclone formation (Nova Scotia near 45N-62.5W)

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