MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #43 (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.**********
...WEDNESDAY JULY 7 2021 10:30 PM EDT...
Satellite image as of 2240Z. 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 1200Z:
Note that the weekend edition posts (without the computer model summary and above-style charts created by mobile phone) will continue this week as I am currently on vacation.
See Tropical Storm Elsa section below for additional details on the storm. Elsewhere…a tropical wave of low pressure in the eastern tropical Atlantic near 35W longitude has seen an increase in thunderstorms earlier today…followed by the formation of a well-defined spin as the thunderstorms have dwindled this evening. Dry Saharan air and also competition with another nearby tropical wave to the east will make conditions challenging for development…and none of the recent runs of global models forecasted this wave to develop.
The upper ridge that was over western North America…associated with last week’s record breaking heat over the northwest US and western Canada…has since been split into two cells…one currently over the northwest Atlantic…the other over the southwest US. Split flow upper divergence between the upper vorticity lingering over the southeast US and the southwest US upper ridge cell triggered thunderstorms across southern Texas over the last day or so. Recently…this area of activity has evolved into a somewhat organized tropical low pressure located over coastal Texas…aided further by the upper divergence zone on the south side of a smaller lobe of upper vorticity located on the west side of the larger scale southeast US upper vorticity. This tropical low pressure area is not likely to develop into a tropical depression as the surface steering flow on the west side of the Atlantic surface ridge is likely to push this system north into land…however heavy rainfall with flash flooding potential is possible over coastal Texas (note flash flood advisories are posted here as of this writing).
TROPICAL STORM ELSA...Over the last 24 hours…Elsa became a hurricane briefly for a second time while located just offshore of western Florida (the first time was on Friday July 2 when Elsa passed near Barbados… St Vincent… and St Lucia). Elsa achieved its second hurricane peak by firing a thunderstorm flare over and just east of its center while aided by divergent upper flow on the east side of the upper vorticity over the northern Gulf of Mexico and southeast US. The strongest thunderstorms soon broke away to the north and east of the center as the upper flow was also shearing in nature…which caused Elsa to drop below hurricane force. Just before the center made landfall near Steinhatchee Florida in the late morning hours…the tropical storm was able to maintain 65 mph maximum sustained winds while firing another organized thunderstorm mass over and east of the center. This mass has more or less persisted after landfall as Elsa moves across southeast Georgia tonight while Elsa remains supported by the divergent nature of the upper flow…thus Elsa has only slowly weakened to 45 mph max sustained winds as of 8 PM EDT.
The forecast track remains unchanged thru 24 hours…and then is faster by 48 hours as the models have converged on a faster speed for that timeframe. For the remainder of its life…Elsa will continue northeast in deep-layer southwesterly flow around the west side of the Atlantic surface ridge and out ahead of the upper vorticity over the southeast US…with the upper layer of southwesterly flow to be re-enforced by the arrival of the next upper trough currently incoming from Central North America. The intensity forecast still shows Elsa hanging on as a tropical cyclone enhanced by the divergent nature of the upper flow as Elsa’s center moves inland across the Carolinas…and I agree with the NHC lowering the intensity forecast over the Carolinas to 35 mph maximum sustained winds (a tropical depression) as Elsa made landfall slightly weaker and below hurricane force. By 48 hours…the center of Elsa is forecast to be over cooler waters just offshore of the northeast US…and the cold front associated with the incoming central North America upper trough will overspread Elsa…thus I forecast transition into a non-tropical frontal cyclone at that time. Some re-strengthening of Elsa as a non-tropical frontal cyclone is expected as Elsa encounters less surface friction over water…and as the upper divergence zone associated with the incoming central North America upper trough will be stronger than the upper divergence zone of the southeast US upper vorticity. With these forecast updates:
(1) Preparations for possible tropical storm conditions across southeast Georgia and the coastal Carolinas should have been completed by now…although Elsa is now expected to cross the Carolinas as a tropical depression as discussed earlier:
**Elsa will affect southeast Georgia thru tonight…then the eastern Carolinas thru tomorrow (Thursday).
**Elsa will bring some gusty winds across the coastal Carolinas and coastal Georgia going forward. Given the current strength of Elsa and its forecast weakening to a tropical depression…wind damage is only expected to be very isolated. Also expect some coastal surf and rip currents
**Where land friction is higher…inland over the eastern Carolinas and eastern Georgia…wind will only be breezy at worst and wind damage potential is extremely low.
**Heavy rain with flash flooding potential is expected across southeast Georgia and the eastern Carolinas
**Surface southerly flow on the east side of Elsa and upper southwesterly flow over Elsa will create wind shear and thus tornado potential east of Elsa’s center. Tornado watches are likely to continue across southeast Georgia and the eastern Carolinas
(2) Here are some of the strongest north Florida National weather service station reports of wind (in mph) over the last few hours:
**St Petersburg…sustained 13…gust 23 (8:53 PM EDT)
**Lakeland…sustained 14…gust 28 (4:50 PM EDT)
**Spring Hill…sustained 14…gust 20 (6:53 PM EDT)
**Gainesville…sustained 22…gust 37 (1:53 PM EDT)
**Lake City…sustained 15…gust 29 (5:55 PM EDT)
**Jacksonville…sustained 28…gust 43 (4:53 PM EDT)
**The estimated 65 mph max sustained winds Elsa made landfall with near Cedar Key and Steinhatchee were likely missed by the National weather service stations
(3) Here are some of the strongest southeast Georgia National weather service station reports of wind (in mph) over the last few hours:
**Waycross…sustained 17…gust 30 (now)
**Valdosta…sustained 26…gust 41 (1:53 PM EDT)
**Brunswick…sustained 15…gust 48 (7:53 PM EDT)
**Savannah…sustained 13…gust 22 (2:56 PM EDT)
(4) Interests across the northeastern US coastal region should now be preparing for Elsa as it has potential to re-strengthen as a non-tropical frontal cyclone. The remnant cyclone is expected to move quickly across the region on Friday:
**Heavy rainfall with flash flooding potential expected from eastern Virginia to Maine
**Gusty winds with some damage potential expected from coastal Virginia to coastal Massachusetts…prepare for possible power outages if you live in a community with above-ground power lines
**Coastal sea swells from coastal Virginia to coastal Maine are expected.
(5) Interests across Nova Scotia and Newfoundland can also expect gusty winds…coastal sea swells…and heavy rainfall from the remnant frontal cyclone of Elsa on Saturday.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Jul 8)…45 mph maximum sustained wind tropical storm centered over the Florida/Georgia border at 31.4N-82.7W
IOH 24 Hr Forecast (0000Z Jul 9)…35 mph maximum sustained wind tropical depression centered over the eastern part of the North Carolina/Virginia border at 36.2N-77W
IOH 48 Hr Forecast (0000Z Jul 10)…Frontal cyclone centered between Massachusetts and Nova Scotia at 42.2N-67.5W