MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #25 (Weekend Edition)
*******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 media...watches 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.gov (hurricanes dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********
...SATURDAY JUNE 19 2021 11:48 PM EDT...
Satellite image as of 0120Z. 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 1800Z:
GFS Model Upper-Level Winds 1800Z:
See Claudette section below for an update on the tropical cyclone…which is continuing to churn across the southeast United States. 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 as far west as 25W longitude. 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 some of the CMC…NAVGEM…and GFS 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.
TROPICAL DEPRESSION CLAUDETTE...Since special update #24A this past afternoon…Claudette has weakened to a tropical depression while the center is accelerating eastward across Alabama. Since landfall…Claudette has been aided by the divergence zone of lingering central US 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 Claudette is no longer over water and thus the thunderstorms do not have as much moisture and thus are not releasing as much latent heat when the water vapor condenses into clouds…thus Claudette weakened to a tropical depression after landfall as a typical tropical system should. But at the same time Claudette is not expected to weaken further as the aforementioned processes keep it going over land…and when it arrives to the Carolina coast where it begins to tap into warm Gulf Stream Atlantic water…it is all but certain at this point that the thunderstorms will get enough moisture and release enough latent heat of condensation to bring Claudette back to tropical storm strength. Thus I have issued an intensity forecast below instead of a probability outlook on tropical storm formation as I previously planned.
The central US vorticity is moving faster to the east than previously anticipated…and since this is a primary feature supporting Claudette over land the result it that Claudette is also moving faster to the east than previously forecast…thus my updated forecast track brings Claudette to the Carolina coast tomorrow night instead of Monday. 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 Monday 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 Monday evening for Claudette to reach a peak strength of 60 mph max sustained winds right as it exits the warm Gulf Stream waters. 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…on Claudette’s now faster forecast track…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:
**with the updated intensity forecast…winds over Alabama…Georgia…and inland portions of the Carolinas should be breezy but only produce very isolated damage over the next 24 hours. The coastal Carolinas are more likely to see the formation of a tropical storm wind field and during tomorrow night which will have a little more damage potential…but damage will still tend to be isolated.
**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 latest outlook discussed above…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 low.
**Based on the latest doppler radar…thru the remainder of this weekend the area of heavy rainfall with flash flooding potential is narrowed down to Alabama…Georgia…southeastern Tennessee… the Carolinas… and southern Virginia. Should you encounter a flooded road…do not drive into the water or your vehicle could become stuck and you could drown.
**The surface southerly flow on the east side of Claudette combined with upper westerly winds over the SE US is producing shear favoring tornadoes. A tornado watch is in effect for the western Florida panhandle… SE Alabama… and SW Georgia as of this writing. It would not surprise me if additional tornado watches are issued in SE Georgia and the Carolinas for the remainder of this weekend.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Jun 19)...35 mph maximum sustained wind tropical depression centered over central Alabama at 32.4N-87.7W
IOH 24 Hr Forecast (1800Z Jun 20)...40 mph maximum sustained wind tropical storm centered on the Carolina coast…at the NC/SC border…at 34N-79W
IOH 48 Hr Forecast (1800Z Jun 21)…60 mph maximum sustained wind tropical storm centered offshore of the US New England Coast at 39N-70W
IOH 72 Hr Forecast (1800Z Jun 22)…Remnant low centered between Nova Scotia and Newfoundland at 46N-59W