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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.**********

...FRIDAY OCTOBER 18 2019 4:00 PM EDT...

See Tropical Storm Nestor section below for more details on the only active tropical cyclone in the Atlantic basin. See area of interest sections below for all areas being monitored for tropical cyclone formation.

TROPICAL STORM NESTOR...The intensifying broad surface low pressure in the Gulf of Mexico has finally been upgraded to Tropical Storm Nestor. Previously this stregnthening circulation was not considered a tropical storm due its north-south elongation that had multiple spins...with the northern part of that circulation supported non-tropically by divergence on the east side of the cut-off upper trough which is currenlty moving across Louisiana...and the southern part of that circulation supported by outflow of warm Gulf of Mexico upper ridging out ahead of the cut-off upper trough and to the southeast bolstered by the ongoing tremendous thundersorm latent heat release. Air temperature constrasts across the circulation have reduced as indicated by the front around the circulation being removed in the National Hurricane Center surface analysis...and a rather impressive circular thunderstorm complex just east of the circulation center has been in progress all day today such that the National Hurricane Center considers this system a tropical feature. The very recent upgrade to tropical storm status is due to the elongated circulation developing a better defined center. Newly-declared Tropical Storm Nestor in the next 48 hours will bring heavy rains with possible flash flooding...coastal storm surge...and gusty winds capable of power outages and some damage to southern Alabama...northern Florida...southern Georgia...the southeastern half of South Carolina...and the coastal plain region of eastern North Carolina. Preparations here should be rushed to completion today...but the aforementioned interests in the Carolinas will have some time to prepare on Saturday as the worst conditions are expected on Sunday. Even though my previous track forecast so far has been quiet on updated forecast track is nudged northwestward to account for the 11 AM EDT NHC forecast track and continued more northward trajectory in the 1200Z GFS model run...but I am not convinced just yet of this system being quiet as far north as shown in the 1200Z GFS as a look at the same model's upper-level wind field shows to me the maximum upper divergence zone of the cut-off upper trough being further south. Over the next 48 hours Nestor will not be a conventional tropical storm...potentially retaining its current strength even with landfall across northern Florida and southern Georgia due to the support of the cut-off upper trough. After that Nestor settles on the west side of the fast-moving surface ridge currently over the eastern US...the ridge appears it will block Nestor from moving eastward out to sea...likely bending the track of Nestor northward parallel to the eastern US coast. And during this time as the cut-off upper trough shifts southeastward and away while warm core upper ridging builds overhead in warm air advection ahead of two strong frontal lows forecast to eject from the western US into Canada during the forecast period...I show weakening to 50 mph maximum sustained winds despite the low shear under the upper ridging due to a potential brief burst of shear when the cut-off upper trough moves through the circulation of Nestor...and as a slight change in track would move Nestor into cooler waters on either side of the warm Gulf stream. The latest model runs show the pair of frontal lows ejecting from the western US being further west...with Nestor getting trapped in weak steering at 72 to 96 hours between the surface ridgign to the east and new surface ridging building to the north under the western convergence of the upper trough associated with the first of the two frontal lows passing by to the north..but I speculate a westward drift will occur during that time as the second of the two frontal lows drops surface pressures to the west while significantly intensifying. By 120 hours for now I show a northeastward track toward Cape Cod Masschusetts while the second frontal low captures this system...and show no weakening as the amplfied upper trough of the frontal low potentially supports Nestor while transitioning it to a non-tropical gale along the frontal low's cold front.

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

0 Hr Position...60 mph maximum sustained wind broad surface low in the central Gulf of Mexico centered at 25.9N-90W

IOH 24 Hr Forecast (1200Z Oct 19)...65 mph maximum sustained wind tropical storm centered over the Florida panhandle coast at 30N-83.2W

IOH 48 Hr Forecast (1200Z Oct 20)...65 mph maximum sustained wind tropical storm centered just southeast of Wilmington North Carolina at 33N-76.5W

IOH 72 Hr Forecast (1200Z Oct 21)...50 mph maximum sustained wind tropical storm centered offshore of the eastern United States at 36.5N-72W)

IOH 96 Hr Forecast (1200Z Oct 22)...50 mph maximum sustained wind tropical storm centered offshore of Maryland...Delaware...and New Jersey at 37N-73W

IOH 120 Hr Forecast (1200Z Oct 23)...50 mph maximum sustained wind non-tropical remnant gale centered over Cape Cod Massachusetts at 41N-70W

AREA OF INTEREST 1...Upgraded to Tropical Storm Nestor while putting this post together. See Tropical Storm Nestor section above for details.

AREA OF INTEREST #2...The tropical wave crossing the Lesser Antilles continues featuring bursts of showers and thunderstorms while moving into the eastern Caribbean Sea due to divergence on the east side of a sharp cut-off upper trough in the area. The latent heat release of the thunderstorm activity has begun splitting the upper trough into two smaller upper vortices. Therefore it now appears this area of disturbed weather is more likely to continue westward through the Caribbean Sea during the next five days...and my updated outlook positions below are notably shifted southwestward. The upper-level wind forecast looks favorable to this tropical wave as the western of the two small upper vortices is likely to retrograde westward and away in expansive upper ridging to build ahead of two strong frontal lows to eject from the western US into Canada during the five day forecast period. However computer models continue to not be on board for showing tropical cyclone I only have slowly increasing odds of development in my updated outlook. Regarding the track of this disturbance...the current southeastern Canada frontal cyclone...Tropical Storm Nestor...and the two forecast western US-to-Canada frontal lows are forecast to quickly eject too far north to influence the steering...thus leaving this system to continue west-northwest under the tropical surface low-latitude easterlies during the forecast period. Regardless of tropical cyclone formation or not...this tropical wave has potential to bring heavy rainfall to Puerto Rico...the Virgin Islands...Dominican Republic...Haiti...Jamaica...and the Cayman Islands in the coming days.

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

IOH 24 Hr Oulook (1200Z Oct 18)...0% chance of tropical cyclone formation (eastern Caribbean Sea near 15N-66W)

IOH 48 Hr Oulook (1200Z Oct 19)...5% chance of tropical cyclone formation (just south of the Dominican Republic near 16N-70W)

IOH 72 Hr Oulook (1200Z Oct 20)...10% chance of tropical cyclone formation (southeast of Jamaica near 17N-75W)

IOH 96 Hr Oulook (1200Z Oct 21)...15% chance of tropical cyclone formation (southwest of Jamaica and south of the Cayman Islands near 18N-79W)

IOH 120 Hr Outlook (1200Z Oct 22)...20% chance of tropical cyclone formation (southwest of the Cayman Islands near 19N-83W)

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