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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.**********

...SUNDAY JUNE 20 2021 11:40 PM EDT...

Satellite image as of 0310Z. Areas of interest circled in yellow are not mentioned in the NHC tropical weather outlook. Areas circled in a green dashed line are in the NHC 5-day tropical weather outlook. Areas circled in a solid green line are in the NHC 2-day tropical weather outlook:

NHC TAFB Surface Analysis 1200Z:

GFS Model Upper-Level Winds 1800Z:

See Claudette section below for an update on the tropical cyclone…which is continuing to churn across the Carolinas and will be entering the western Atlantic by tomorrow morning. Elsewhere…conditions in the eastern tropical Atlantic have improved again for potential development as dry Saharan air has been weakened by tropical waves of low pressure emerging from Africa that are producing rotating thunderstorm clusters. Models forecast that the upper ridge in the region keeping shear low and outflow high will be in place for the next several days…and the 1200Z CMC…1800Z NAVGEM…1200Z GFS… and 1200Z ECMWF model runs hinted at development in this region in about a week. Therefore will be keeping an eye on this region in the coming days.

In addition…models agree that the upper trough currently over southeast Canada may evolve into a cold cut-off upper vortex near or over the Azores in about 4 to 5 days…potentially cold enough to support thunderstorms and tropical characteristics for any surface low pressure generated by the vortex. Therefore the Azores region may become another area of interest in the coming days.

TROPICAL DEPRESSION CLAUDETTE...While sliding east-northeast state-by-state across the southeastern United States…Claudette has been aided by the divergence zone of lingering upper vorticity to the west…which has kept its surface pressure low and helped Claudette to keep thunderstorms firing. In turn the thunderstorm latent heat release is boosting warm upper ridging whose resulting outflow is also helping to keep Claudette going. It’s just that by being over land… the thunderstorms have not had as much moisture and thus are not releasing as much latent heat when the water vapor condenses into clouds…thus Claudette has not strengthened tropically over land which is normal. Claudette is now passing through the Carolinas and by tomorrow morning will be entering the western Atlantic where it will begin to tap into warm Gulf Stream water…and it is fairly certain that the thunderstorms will get enough moisture and release enough latent heat of condensation to bring Claudette to tropical storm strength. In fact Claudette may already be feeding off the warm Gulf Stream waters as the skeletal thunderstorm bands on its east side have begun to re-strengthen and the NHC has recently bumped up Claudette’s max sustained winds from 30 to 35 mph as of 11 PM EDT.

Claudette is north and west of my previous forecast…and my updated one is adjusted accordingly. Once Claudette moves offshore…the track is forecast to bend more north on a general course parallel to the US northeast coast due to the stout presence of the Atlantic surface ridge to the east. Also the supporting cold core upper vorticity will dissipate by tomorrow as the atmosphere is warmed by the warm sector of the currently developing central Canada frontal low. This could result in more warm upper ridging forming over Claudette with low shear and upper outflow…thus I forecast by tomorrow evening for Claudette to reach a peak strength of 50 mph max sustained winds right as it exits the warm Gulf Stream waters. This is lower than my previous intensity forecast as Claudette is below my previous intensity forecast. By Tuesday as Claudette approaches Atlantic Canada (Nova Scotia and Newfoundland)…I currently forecast a weak remnant low due to much cooler waters and as the upper trough supporting the central Canada frontal low will be too far west to aid Claudette’s remnants with its eastern divergence zone.

Here is the latest Outlook on Claudette’s impact potential with this updated forecast:

**The latest weather station observations suggest breezy conditions developing across coastal southeastern North Carolina from Cape Hatteras and points south…as well as coastal northeastern South Carolina. This region is on the south side of Claudette where winds are aided by the east-northeast motion of the storm…and as Claudette re-strengthens overnight this is the coastal region where the formation of a tropical storm wind field is possible…with such a wind field producing isolated damage.

**Quickly passing coastal sea swells and rip currents as well as offshore choppy seas are likely Monday through Tuesday from the Carolinas through New England on the US Atlantic coast…and the Nova Scotia coast. Based on the above outlook…the chances for Claudette to kick up the seas on coastal Newfoundland is low due to forecast weakening….and also the chance for Claudette to bring winds directly to Newfoundland and Nova Scotia is also low as a result of the forecast weakening.

**Based on the latest doppler radar…the best chance for isolated flash flooding going forward is over southeast North Carolina as the remainder of Claudette’s now singular curved rain band is moving offshore from South Carolina. In the event you do encounter a flooded road…do not drive into the water or your vehicle could become stuck and you could drown.

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

0 Hr Position (1800Z Jun 20)...35 mph maximum sustained wind tropical depression centered inland near the NC/SC border…at 34.7N-80.4W

IOH 24 Hr Forecast (1800Z Jun 21)…50 mph maximum sustained wind tropical storm centered offshore of the US New England Coast at 38N-72W

IOH 48 Hr Forecast (1800Z Jun 22)…Remnant low centered just offshore of eastern Nova Scotia at 44.5N-61.2W

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