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 #133 (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 OCTOBER 10 2021 11:50 AM EDT...

Satellite image as of 0500Z. 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 (Saturday Oct 9):

GFS Model Upper-Level Winds 1800Z (Saturday Oct 9):


See area of interest sections below for areas being watched for development in the Atlantic tropics.


AREA OF INTEREST #1... The central Atlantic tropical wave of low pressure that crossed the Lesser Antilles a couple of days ago has moved quickly west into the central Caribbean Sea…. faster than I anticipated. Although thunderstorm activity has increased near the northern apex of the wave… in the vicinity of the southeastern Bahamas with the support of the divergence zone associated with the upper vorticity emerging from the eastern US… the surface inflow of area of interest #2 will dominate the region and tropical development is not anticipated here. There are no longer any model runs that show development of this wave either. Had the wave moved slower and kept its distance from area of interest #2… then development may have been possible. This is my final statement on this tropical wave on this blog as an area of interest. Note that heavy rainfall may occur across the southeastern Bahamas within the next day or so.


AREA OF INTEREST #2...The surface low pressure area offshore of the southeastern US has become better defined this weekend while strengthening under the supportive eastern divergence zone of the amplified upper vorticity approaching from the eastern US. Aircraft recon on Saturday had investigated this system when it had more widespread thunderstorm activity but did not find a well-defined surface spin. A well-defined swirl has developed on satellite pictures as of late to the east-southeast of Cape Lookout North Carolina… located at 34N-75.5W as of 0600Z… however the overall thunderstorm activity of this system has dwindled and is lacking near this swirl center. As a result this system is not classified as a subtropical cyclone at present. I agree with the NHC outlook’s 50% odds of development in the next 24 hours as the surface low will remain under the eastern divergence zone of the upper vorticity… which could allow it to fire thunderstorms near the swirl center and become a subtropical cyclone (note the NHC has recently at 8 AM EDT dropped development odds to 30% as thunderstorm activity has still not developed near the swirl center… I am keeping my development odds at 50% at this time). The surface low is seen drifting north toward the North Carolina Outer Banks on satellite and Doppler radar… therefore my 24-hour forecast point therefore assumes the center will be over or near Cape Hatteras. My updated outlook below has switched from a tropical to a subtropical designation as the upper vorticity is fast approaching… making this system more likely to a subtropical feature supported by the upper vorticity and less likely to become a tropical feature that develops a warm core upper outflow just to the east of the upper vorticity.

The upper vorticity after 24 hours will split into two halves… with the south part settling over the western Bahamas and the north part becoming a shortwave upper trough that accelerates east toward the current northwest Atlantic upper trough. It will be difficult for this system to accelerate east with the shortwave upper trough as the strong surface ridge to the north will try to pin it down… however given the current north drift of this system it is likely that this system will at least drift east by 48 hours while chasing a frontal low to develop in the eastern divergence zone of the shortwave upper trough. Therefore I agree with the track solution shown in the 0000Z GFS model run. I drop development odds to 0% at 48 hours as this system will encounter increased westerly shear and upper convergence on the west side of the shortwave upper trough as it fails to accelerate rapidly east with the trough.

With these forecast updates:

**Even without the formation of a subtropical cyclone… the pressure difference between this system and surface ridge to the north is resulting in strong onshore winds that are kicking up the surf across the mid-Atlantic and northeast US coast. This pattern will last for another 24 hours after which time this system low is forecast to weaken as discussed above.

**The gusty onshore winds have reached areas from North Carolina to the coastal northeast US… and will be possible in this region in the next 24 hours.

**Periods of heavy rainfall are possible for the coastal mid-Atlantic and northeast US.


Here are some recent National Weather Service station observations of wind (mph):

**Wilmington NC… sustained 16… gust 29 (9:53 AM EDT)

**Morehead City NC… sustained 22… gust 32 (4:58 AM EDT)

** Morehead City NC… sustained 16… gust 26 (now)

**Hatteras NC… sustained 14… gust 29 (12:51 AM EDT)

**Virginia Beach VA… sustained 15… gust 29 (4:56 AM EDT)

**Virginia Beach VA… sustained 18… gust 28 (now)

**Ocean City MD… sustained 16… gust 26 (now)

**Dover DE… sustained 15 (now)

**Atlantic City NJ… sustained 15… gust 24 (8:54 AM EDT)

**New York NY… sustained 12… gust 20 (now)

**Bridgeport CT… sustained 14 (now)

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

IOH 24 Hr Outlook (0600Z Oct 11)… 50% chance of subtropical cyclone formation (Cape Hatteras North Carolina near 35.5N-75.5W)

IOH 48 Hr Outlook (0600Z Oct 12)… 0% chance of subtropical cyclone formation (offshore of the mid-Atlantic US near 36N-72.5W)


AREA OF INTEREST #3… A tropical wave of low pressure has spent the last couple of days moving into the Central tropical Atlantic from the eastern Atlantic. The wave has become better defined and organized with increased concentrated thunderstorm activity… which suggested the lowest pressure of the wave is near 10.5N-48W. Although this is toward the west side of the thunderstorms due to light northwesterly shear… the wave will soon be heading to a low shear and upper outflow environment beneath the current central Atlantic upper ridge… and the ridge will be expanding as the west Atlantic upper vorticity continues to weaken. Moreover various model runs suggest this wave could develop… therefore I have added this tropical wave as an area of interest in this update.


The tropical wave’s track is expected to increasingly slow down and bend north due to an expanding surface ridge weakness to be caused by the remnants of Area of Interest #2… a frontal low to the east of Area of Interest #2 to be generated by the eastern divergence zone of the current upper vorticity emerging from the eastern US… and will be continued by the eastern divergence zone of the current central US upper trough once that trough moves into the west Atlantic over the next few days. I already have peak 40% development odds as the wave has some signs of organization and the upper air pattern will be conducive for development as discussed above. However by day 5 I trim down development odds as the north track of the wave brings it toward westerly shearing winds to be generated out ahead of the aforementioned upper trough that arrives from its current position over the central US. I recommend Interests in the Lesser Antilles monitor the progress of this wave as the forecast track brings the wave rather close to the islands by days 3 to 4. Even if tropical cyclone development does not occur… heavy rains and gusty winds are possible.

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

IOH 24 Hr Outlook (0600Z Oct 11)… 10% chance of tropical cyclone formation (central tropical Atlantic near 11.5N-52W)

IOH 48 Hr Outlook (0600Z Oct 12)… 20% chance of tropical cyclone formation (east of the Lesser Antilles near 12.5N-57W)

IOH 72 Hr Outlook (0600Z Oct 13)… 30% chance of tropical cyclone formation (just east of the Lesser Antilles near 15.5N-60W)

IOH 96 Hr Outlook (0600Z Oct 14)… 40% chance of tropical cyclone formation (just east of the northern Lesser Antilles near 17.5N-61W)

IOH 120 Hr Outlook (0600Z Oct 15)… 30% chance of tropical cyclone formation (northeast of the Lesser Antilles near 20N-60W)

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