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 OCTOBER 6 2019 3:39 PM EDT...

See area of interest sections below for areas being monitored for tropical and subtropical cyclone formation. Elsewhere...the showers and thunderstorms in the northwestern Caribbean Sea that have persisted under the outflow of an upper ridge cell in the area continues to have a surface trough of low pressure. model support showing tropical development is not present...and conditions for development will become less favorable by 2 days as southwesterly shear increases from the upper trough currently over central North America. Regardless of development...the eastern upper divergence zone of this upper trough could cause the mositure from this disturbance to spread northward from western Cuba and the Cayman Islands into the Florida peninsula and western Bahamas by 2 days...with flash flooding possible in any heavy persistent rainfall.

AREA OF INTEREST #1...The tropical wave southwest of the Republic of Cabo Verde Islands continues to produce showers and thunderstorms. Because its associated activity still has not become better organized...I have lowered odds of tropical cyclone development to 0%. Although upper-level winds are currently favorable for tropical development as an expansive upper ridge cell (with low shear and upper outflow) persists over the eastern Atlantic...this tropical wave will soon reach unfavorable shear from lingering central Atlantic upper vorticity in 72 hours. This is my final statement on this tropical wave as an area of interest on this blog.

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

IOH 24 Hr Outlook (1800Z Oct 7)...0% chance of tropical cyclone formation (tropical Atlantic near 32.5W)

IOH 48 Hr Outlook (1800Z Oct 8)...0% chance of tropical cyclone formation (tropical Atlantic near 37.5W)

IOH 72 Hr Outlook (1800Z Oct 9)...0% chance of tropical cyclone formation (tropical Atlantic near 42.5W)

AREA OF INTEREST #2...Surface cold front and upper trough in the central Atlantic to evolve into a cut-off deep-layered low pressure that will likely acquire tropical characterstics...have begun a subtropical cyclone formation as outlined below. At the surface...the cut-off is expected to be induced by a strong surface ridge to build in the central Atlantic due to increasing western convergence of the sharpening upper trough...and the upper trough is expected to sharpen with a portion of the trough becoming a cut-off upper vortex due to broad upper ridging amplifying to the west in warm surface southerly flow ahead of a strong central Canada frontal cyclone. The surface and upper-level ridging is expected to drive the resulting cut-off deep-layered low pressure west-southwestward by days 2 and 3. Although the surface circulation will reach the ridge weakness of the system in area of interest #3 by day 4...I hang on to a southward angle in the forecast track by that time as the circulation reaches the west side of the cut-off upper vortex where some northerly upper winds could affect the steering...and then turn this system northwest by 120 hours (day 5) into the ridge weakness after escaping the influence of the upper vortex. My forecast track is adjusted westward due to the current position of the surface cold front area which will later evolve into the cut-off deep-layered low. Although the cut-off deep-layered low is expected to initially form over waters typically too cool for tropical development...the cold temperatures of the cut-off upper vortex are likely to de-stabilize the atmosphere for thunderstorm activity and tropical characteristics to develop. I begin to show weakening at 96 hours while the surface circulation moves into the less favorable convergent west side of the cut-off upper vortex. At 120+ hours this system is likely to lose its identity to the low pressure field of area of interest #3...but will be moving into favorable upper winds directly below an upper ridge cell induced by warm air advection ahead of area of interest #3. Therefore I do wonder if there is potential for this system to make the transition from subtropical to fully tropical before fully losing its identity.

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

0 Hr Position (1800Z Oct 6)...Cold front in vicinity of 32.5N-50W

IOH 24 Hr Forecast (1800Z Oct 7)...Frontal low centered at 32.5N-40.5W

IOH 48 Hr Forecast (1800Z Oct 8)...Frontal low acquiring tropical characteristics...centered at 31N-45W

IOH 72 Hr Forecast (1800Z Oct 9)...50 mph maximum sustained wind subtrpoical storm centered at 30N-51W

IOH 96 Hr Forecast (1800Z Oct 10)...35 mph maximum sustained wind subtropical depression centered at 29N-55W

IOH 120 Hr Forecast (1800Z Oct 11)...Remnant low centered at 31N-58W

AREA OF INTEREST #3...An area of rotating showers and thunderstorms currently north of the Bahamas...featuring a new surface trough of low supported by divergence on the northeast side of a cut-off upper vortex at the present time. This disturbance continues to be in the 5-day National Hurricane Center tropical weather outlook as this disturbance has a decent chance to evolve into a formidable subtropical cyclone just offshore of the northeastern US in about 4 to 5 days. This disturbance appears it will continue slowly drift northward or northwestward in the short-term under the influence of the strong surface ridge that has moved into the western Atlantic...and as the cut-off upper vortex gravitates northwestward toward and eventually merges with the sharp upper trough currently over central North America. The merger should be underway by 24 hours as the upper trough arrives into the eastern US...upon which time a tremendous area of upper divergence on the east side of the merged upper trough as well as outflow of upper ridging to the east should cause the surface trough to strengthen. By 48 hours...whatever surface low pressure forms from the surface trough will have merged with the cold front of the merged upper trough...making this disturbance initially lose tropical characteristics. What happens after 48 hours should get quiet interesting at a location northwest of Bermuda and offshore of the eastern US the CMC...NAVGEM...Euro...and GFS models all strongly agree a round of amplifying warm deep-layered ridging to the west and north should cut-off the tremendous merged upper trough into a rather impressive upper vortex...with this disturbance having a decent chance to evolve into a large and strong subtropical cyclone whose thunderstorms would be supported by the cold temepratures of the upper vortex depsite being over mild water temperatures. The warm deep-layered ridging during that timeframe looks like it will be induced by plenty of warm air advection ahead of another strong forecast frontal cyclone to form over central Canada (currently the energy for this forecast frontal cyclone lies with an upper vortex over Alaska). My peak 120-hour odds of subtropical cyclone formation are raised to 70% due to the strong computer model agreement...and I plan to begin a subtropical cyclone formation forecast if the model consensus continues.

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

IOH 24 Hr Outlook (1800Z Oct 7)...0% chance of subtropical cyclone formation (western Atlantic near 29N-69.5W)

IOH 48 Hr Outlook (1800Z Oct 8)...0% chance of subtropical cyclone formation (western Atlantic near 35N-70W)

IOH 72 Hr Outlook (1800Z Oct 9)...0% chance of subtropical cyclone formation (western Atlantic offshore of the northeastern US coast near 37.5N-67.5W)

IOH 96 Hr Outlook (1800Z Oct 10)...50% chance of subtropical cyclone formation (south of Cape Cod Massachusetts near 37.5N-70W)

IOH 120 Hr Outlook (1800Z Oct 11)...70% chance of subtropical cyclone formation (offshore of New Jersey and Delaware near 37.5N-71W)

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