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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 

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*******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.**********

...TUESDSAY OCTOBER 8 2019 3:08 PM EDT...

See area of interest sections below for areas being monitored for tropical and subtropical cyclone formation. Elsewhere...showers and thunderstorms are increasing in the vicinity of the southern Lesser Antilles and coastal Venezuela due to split flow upper divergence between the southwest side of a large upper vortex coming together over the central Atlantic and upper ridging over the western Atlantic. This warm upper ridging will strengthen in warm southerly flow ahead of area of interest #2...which should cause a portion of the central Atlantic upper vortex to cut-off and head westward across the Caribbean. Thus a general wave of thunderstorm activity is likely to continue and head westward into the Caribbean due to enhanced upper outflow between the smaller cut-off vortex and larger central Atlantic vortex...and the GFS and CMC models have been suggesting that tropical cyclone development could occur in this activity. If the reliable Euro (ECMWF) model joins in showing such a solution...then I will be introducing this activity as yet another area of interest for tropical development in my next update.

AREA OF INTEREST #1...The south portion of a cold front and upper trough moving across the central Atlantic has become a cut-off frontal deep-layered low pressure...with the cut-off being triggered by deep-layered ridging passing to the north. This deep-layered ridging is induced by warm upper ridging bolstered by the warm southerly flow ahead of strong eastern Canada surface frontal low...with convergence on the southeast side of the upper ridging producing a strong surface ridge. The deep-layered ridging is expected to drive the cut-off deep-layered low pressure west-southwestward in the next 24 hours. Although the surface circulation of the deep-layered low will reach the surface ridge weakness of the system in area of interest #2 by 48 hours...I hang on to a southward angle in the forecast track by that time as the surface circulation reaches the west side of the upper part of the circulation where some northerly upper winds could affect the steering. I then turn this system northwest by 72 hours into the ridge weakness after the surface circulation completely decouples and escapes the upper-level circulation. My forecast track is nudged northward due to the current position of the surface circulation of the deep-layered low. So far the surface circulation lacks strong thunderstorm activity...perhaps as the cold temperatures of the upper circulation (upper vortex) are not quiet cold enough for stronger thunderstorms. However the instability will increase as the surface circulation moves west-southwest toward warmer waters in the next 24 hours...thus I still forecast transition to a subtropical storm. I continue to suggest an initial intensity of 50 mph maximum sustained recent ASCAT passes show maximum winds of 40 knots (45 mph) on the north side of the circulation and as the surface circulation still remains beneath supportive upper divergence on the east side of the upper circulation...thus I believe the surface circulation could strengthen further to 50 mph maximum sustained winds. I begin to show weakening at 48 hours while the surface circulation moves into the less favorable convergent west side of the upper circulation. At 72+ hours this system is likely to lose its identity to the low pressure field of area of interest #2...but will be moving into favorable upper winds directly below an upper ridge cell induced by warm air advection ahead of area of interest #2. Therefore I do wonder if there is potential for this system to briefly 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 8)...Frontal low centered at 32N-46W

IOH 24 Hr Forecast (1800Z Oct 9)...50 mph maximum sustained wind subtropical storm centered at 30.5N-52W

IOH 48 Hr Forecast (1800Z Oct 10)...35 mph maximum sustained wind subtropical depression centered at 30N-56W

IOH 72 Hr Forecast (1800Z Oct 11)...Remnant low centered at 31.5N-59W

AREA OF INTEREST #2...An area of showers and thunderstorms north of the Bahamas and offshore of the eastern US once supported by a small upper vortex/trough in the region has become entangled with the surface cold front of the large upper trough approaching from eastern North America and also entangled with the surface trough of area of interest #3 approaching from the southwest. Based on the 1200Z NHC TAFB surface analysis and a large arc of clouds seen northeast of area of interest appears that this disturbance has transitioned into a non-tropical low pressure along the cold front...centered just east of Cape Hatteras North Carolina. As this new frontal low interacts with the large amplifying upper trough approaching from eastern North is expected to evolve into a powerful non-tropical cyclone offshore of the eastern US. Therefore regardless of whether or not this system later transtions from non-tropical to subtropical...I recommend preparations on the eastern US coast...particularly on the New England coast...for coastal sea swells to continue as this system will be generating notable ocean effects beginning in 24 hours. I am continuing a subtropical cyclone formation forecast as I believe conditions are going to be favorable for this system to acquire some tropical characteristics in the coming days. A round of amplifying warm deep-layered ridging to the west and north will be responsible for the amplification of the incoming upper trough...with increasing divergence on the east side of the amplifying upper trough rapidly intensifying the the frontal low. This warm deep-layered ridging is already in its early stages as a strengthening surface ridge over the eastern US is supported by convergence on the east side of the central Canada upper ridge...and the central Canada upper ridge will be amplifying in plenty of warm air advection ahead of a strong forecast frontal cyclone to form over central Canada (currently the energy for this forecast frontal cyclone lies with an amplified upper trough over western Canada). My updated forecast points are nudged westward closer to the eastern US coast as the new frontal low appears in the short-term it will be moreso entangled with area of interest #3 approaching from the southwest...because area of interest #3 appears to have surface pressure falls due to the satellite apperance of a very well organized and strong thunderstorm mass. Therefore the threat of damaging winds with power outages appears possible along coastal Massachusetts...Connecticut...Rhode Island...Long Island New York...New Jersey...and Delaware...thus I also recommend preparations here for such impacts to be underway. This system will turn eastward and then northeastward by 72+ hours while moving with the amplified upper trough. The cold temperatures of the upper trough are likely to cause thunderstorm activity despite the mild water temperatures...therefore I forecast transition to a subtropical storm by 72 hours. I show no loss in strength between 72 and 96 hours as this system moves eastward with the supportive eastern divergence zone of the upper trough. This system will likely have a large and strong wind particular on its north side...due to the tight pressure gradient against the deep-layered ridging to form to the north and west. The tremendous wind field on the north side will be blowing towards the northeastern US shore which is why ocean effects (sea swells...storm surge...waves) along the coast are such a concern. By 120 hours...itappears likely that the surface circulation will have whirled directly the upper trough axis where there is a lack of supportive divergence...especially as the upper trough will quickly accelerates northeastward toward the surface circulation...thus weakening and an improvement of ocean conditiosn along the northeastern US coast is expected by then. The cooler water temperatures at the 120 hour forecast position makes it likely that this system will have lost any subtropical characteristics by this timeframe.

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

0 Hr Position (1800Z Oct 8)...Developing frontal low centered just east of Cape Hatteras North Carolina at 35N-75W

IOH 24 Hr Forecast (1800Z Oct 9)...Frontal cyclone centered offshore of the eastern US coast at 36N-70W)

IOH 48 Hr Forecast (1800Z Oct 10)...Frontal cyclone centered south-southwest of Cape Cod Massachusetts at 36N-71W)

IOH 72 Hr Forecast (1800Z Oct 11)...60 mph maximum sustained wind subtropical storm centered south-southeast of Cape Cod Massachusetts near 36N-69W)

IOH 96 Hr Forecast (1800Z Oct 12)...60 mph maximum sustained wind subtropical storm centered at 37.5N-66W

IOH 120 Hr Forecast (1800Z Oct 13)...45 mph maximum sustained wind non-tropical remnant gale centered south of Newfoundland at 42.5N-55W

AREA OF INTEREST #3...The surface trough disturbance that has been producing disturbed weather in the northwestern Caribbean and southeastern Gulf of Mexico regions has lifted northward and now extends into the western Atlantic offshore of the southeastern US while it has transitioned into a feature supported by a vast area of upper-level divergence on the north side of an upper ridge cell that earlier triggered the disturbance and out ahead of a large upper trough approaching from eastern North America. As of this morning and early afternoon...offshore of the southeastern US...a tremendous and well-organized comma shaped thunderstorm mass has formed...with recent ASCAT passes and satellite animation suggesting a 35 knot (40 mph) maximum sustained wind closed surface circulation is developing at 30.5N-76W. The comma shaped thunderstorm mass is sheared eastward from the surface circulation by the upper southwesterly flow ahead of the upper trough. But upper anticyclonic flow just to the east...extending from the north side of the aforementioned upper ridge cell...and perhaps the brisk northeast track of the new circulation keeping up with the upper southwesterly flow...appear to have diminished the effects of the shear such that a tropical depression or weak tropical storm appears to be forming. This is confirmed by the sharp increase in odds in the National Hurricane Center 2 PM EDT tropical weather outlook...therefore I believe it is most likely that this system will be upgraded to a tropical depression or storm later today and thus I have issued a tropical cyclone formation forecast as outlined below. However already by 24 hours...this system should lose its closed circulation to the developing frontal cyclone in area of interest #2...thus technically losing its scientific classification as a tropical cyclone.

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

0 Hr Position (1800Z Oct 8)...Surface trough with developing surface low centered offshore of the southeastern US at 30.5N-76W

IOH 24 Hr Forecast (1800Z Oct 9)...45 mph maximum sustained wind tropical storm at 34N-70W absorbed by frontal cyclone

AREA OF INTEREST #4...The GFS...CMC...NAVGEM...and Euro models continue to suggest that conditions in the eastern tropical Atlantic will favor tropical development in the eastern Atlantic...a tropical wave currently emerging from western Africa is showing signs of organization and widespread thunderstorm activity...therefore I have introduced it as an area of interest for tropical cyclone formation on this blog. I show steadily increasing odds of development as the eastern Atlantic upper ridge cell with low shear and upper outflow will remain in place while the tropical wave moves west under the influence of strong surface subtropical ridging during the 120-hour forecast period. However my 120-hour peak odds of development are only 30% at the present time as the GFS...CMC...and Euro tend to favor the next tropical wave which has yet to emerge from Africa over this wave...only the less-reliable NAVGEM models favors this wave. Perhaps the more reliable models do not develop this tropical wave while predicting the current surge of dry saharan air to the northwest to supress this wave? Perhaps the next wave is more favored due to the potential for this wave to moisten away dry saharan air for the next wave? We shall see in the coming days.

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

IOH 24 Hr Outlook (1800Z Oct 9)...5% chance of tropical cyclone formation (tropical Atlantic offshore of western Africa near 18W)

IOH 48 Hr Outlook (1800Z Oct 10)...15% chance of tropical cyclone formation (tropical Atlantic south of the Republic of Cabo Verde near 23W)

IOH 72 Hr Outlook (1800Z Oct 11)...20% chance of tropical cyclone formation (tropical Atlantic near 28W)

IOH 96 Hr Outlook (1800Z Oct 12)...25% chance of tropical cyclone formation (tropical Atlantic near 33W)

IOH 120 Hr Outlook (1800Z Oct 13)...30% chance of tropical cyclone formation (tropical Atlantic near 38W)

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