BIRDSEYE VIEW POSTS

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 IOHurricanes@outlook.com 

 
 
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MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #40 (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.**********


...SUNDAY JULY 4 2021 7:55 PM EDT...

Satellite image as of 2010Z. 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 0600Z:

GFS Model Upper-Level Winds 0600Z:

See Tropical Storm Elsa section below for additional details on the storm. Elsewhere…tropical waves of low pressure in the eastern and central tropical Atlantic have not shown signs of development while still capped by dry Saharan air…and none of the global models forecast tropical development in the Atlantic basin for the next few days.


TROPICAL STORM ELSA...Over the last 24 hours…despite Elsa slowing down its forward travel the tropical storm has managed to slightly weaken further while roaming the Caribbean waters between Jamaica…Cuba…and Haiti. It was previously thought that by slowing down…this would allow the thunderstorm tops to catch up to and thus align with the surface center and thus strengthening would commence. In addition Elsa is in a low shear and upper outflow beneath an expansive tropical upper ridge cell that would be conducive for strengthening if Elsa would get its act together in terms of its structure.


On its way toward the north Jamaica coastal region…NHC aircraft reconnaissance early today observed a new surface center form beneath the strongest thunderstorm tops that were toward the east that featured a higher surface pressure and thus slightly lower 60 mph max sustained wind than the original center. The central pressure has actually been higher than usual for 60 mph max winds…which indicates the newer center is compact in nature with a tight pressure gradient between it and outside of the storm such that a low central pressure is not needed for higher wind. This new center has passed by the north Jamaican coast and then turned northwest toward eastern and central parts of Cuba as of this evening. True-color satellite has been suggesting throughout the day an organized storm with banding features around the new center. However colorized infrared satellite showed Elsa less organized than yesterday with the strongest thunderstorms in blobs rather than bands…with only very recent colorized infrared finally showing the strongest thunderstorms following a banding pattern. I theorize the earlier disorganization and resultant lack of strengthening was caused by Elsa’s compact new center being small enough to be disrupted notably by Jamaica even with a close by pass (i.e. without a direct landfall).


Despite the formation of a new surface center…Elsa has remained on the previous forecast track and therefore my updated one below is the same as the previous. The northwest turn toward eastern and central Cuba has been caused by the weakening west side of the steering Altantic surface ridge. This part of the ridge is weakening as the eastern North American upper trough and its surface cold front is moving into the west Atlantic. The upper trough will soon leave behind upper vorticity over the northern Gulf of Mexico and southeast US…and the remainder of the upper trough and surface front will soon be leaving the region and allowing the steering surface ridge to somewhat rebuild ahead of the next frontal system to slide across north-central and northeastern North America. That leaves Elsa to be pushed more west by the recovering west side of the surface ridge and move towards central Cuba and Florida Keys…but at the same time Elsa will still likely be strong/tall enough to be pulled north by the lingering upper vorticity over the southeast US/northern Gulf such that the track should be completely due north by 48 and 72 hours. The forecast track line takes Elsa across central Cuba overnight tonight…the Florida Keys tomorrow….then much of the west Florida peninsula coast through 48 hours…and then inland across the eastern US by 72 and 96 hours.


My updated intensity forecast no longer brings Elsa to hurricane strength…and assumes Elsa will weaken slightly across central Cuba in the overnight and then regain 60 mph max winds as it moves into the Florida Keys tomorrow. The current forecast track keeps Elsa toward southwesterly shear to setup ahead of the forecast lingering upper vorticity over the southeast US/northern Gulf…and also ahead of the SW to NE tilted upper trough associated with the next frontal system to slide over north-central/NE North America…thus I forecast Elsa to weaken to 50 mph max winds as it slides along the west Florida peninsula coast by 48 hours. I forecast Elsa to weaken to an inland tropical depression over the southeast US by 72 hours…and then by 96 hours transition into a remnant frontal low moving toward the northeast US coastal region while supported by the divergent east side of the SW to NE tilted upper trough.


With these forecast updates:


(1) For Jamaica…tropical storm force winds have ended. The potential for flash flooding rain will end later tonight.


(2) For the Cayman Islands…given the small wind radius of the current storm center and it’s forecast track…tropical storm force winds are now unlikely tonight. Locally heavy rains and coastal sea swells are still possible from Elsa’s west side


(3) Cuba is experiencing tropical storm force conditions and coastal sea swells in the southeast part of the country. These conditions will spread across central Cuba overnight tonight. Heavy rains with flash flooding potential will be a possibility across much of Cuba tonight.


(4) The western Bahamas are no longer likely to see direct impact from Elsa…however coastal sea swells and locally heavy rain is possible tomorrow from Elsa’s east side.


(5) The Florida peninsula and Keys will likely see tropical storm force conditions on Monday and Tuesday…I recommend preparations should be completed by tonight in the Florida Keys and south half of the Florida peninsula…and be finished by tomorrow morning in the north half of the Florida peninsula. The current forecast track would bring the strongest winds and coastal storm surge across the Keys and along much of the peninsula west side. The east side could still sea swells and rip currents. All of the peninsula could see heavy rains with flash flooding potential.

(6) Interests in the Florida panhandle and along the Georgia and Carolina coasts should still follow Elsa’s progress as impacts are possible in the Tuesday/Wednesday timeframe. However the potential for tropical storm force winds at these locations is decreasing as the forecast track is holding…but coastal sea swells…rip currents…and heavy rainfall will be possible hazards with the current forecast track.

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

0 Hr Position (1800Z Jul 4)…60 mph maximum sustained wind tropical storm centered offshore of eastern Cuba at 19.8N-77.9W

IOH 24 Hr Forecast (1800Z Jul 5)…60 mph maximum sustained wind tropical storm centered between Cuba and the Florida Keys at 24N-81.2W

IOH 48 Hr Forecast (1800Z Jul 6)…50 mph maximum sustained wind tropical storm centered over Tampa Bay Florida at 27.5N-82.5W

IOH 72 Hr Forecast (1800Z Jul 7)…30 mph maximum sustained wind tropical depression centered inland over eastern Georgia at 32N-81.5W

IOH 96 Hr Forecast (1800Z Jul 8)…Remnant frontal low centered over eastern Virginia at 37.5N-77.5W

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