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 #33 (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 JUNE 27 2021 8:50 PM EDT...

Satellite image as of 0020Z. 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 1200Z:

See area of interest sections below for multiple areas being monitored for tropical development in the Atlantic basin. These areas of interest include:

(1) Area of interest #1…tropical wave of low pressure in the eastern tropical Atlantic


(2) Area of interest #2…surface trough of low pressure located in the western Atlantic and supported by upper vorticity in the region…coastal Georgia and southern South Carolina could be affected by tomorrow evening…see area of interest #2 section below for details.


Elsewhere...the upper vortex sliding west across the Gulf of Mexico (under the influence of upper ridging over the eastern US) is already approaching southern Texas and northeastern Mexico…and the surface trough of low pressure associated with this system has relocated northwest under the supportive eastern divergence zone and thunderstorms of the upper vortex. However the thunderstorms have not become organized around the surface trough…and ASCAT passes of surface winds do not reveal a strong surface trough (i.e. a small wind shift and low winds). Therefore I have not declared an area of interest in this region. Of note however…upper winds in the Gulf of Mexico could become more conducive for development over the next day or so as a small upper ridge becomes established over the Gulf of Mexico…once the aforementioned upper vortex makes landfall over south Texas/NE Mexico and relatively higher pressures become established between that vortex and the upper vorticity tied to area of interest #2. If the surface trough or the north end of a tropical wave just to the southeast does take advantage of the small upper ridge’s outflow…a tropical disturbance could still form. Anything that does form would likely be funneled northwest toward the Texas coast while steered by the southwest side of the Atlantic surface ridge…potentially bringing heavy rains over the next day or so.


And finally…another tropical wave of low pressure has entered the eastern tropical Atlantic from Western Africa…and is located east of area of interest #1 with a large but disorganized area of showers and thunderstorms. Various models runs over the last couple of days suggest some development of this wave…for example refer to today’s 1200Z runs of the GFS and ECMWF which developed this wave instead of area of interest #1. Therefore this tropical wave may also emerge as an area of interest for tropical development in the coming days.


AREA OF INTEREST #1…The outer thunderstorm bands of the large eastern Atlantic tropical wave of low pressure appears to have dissipated while succumbing to dry Saharan air in the region. However a small inner core of thunderstorms has developed…therefore this core will either evolve into a small tropical cyclone in the coming days or alternatively also succumb to the dry air. Since either scenario is equally possible…I have only raised odds of development to 50% at this time. Other than dry air…conditions for development are otherwise favorable due to warm waters along the forecast track (26+ deg C) and low shear and upper outflow beneath the tropical upper ridge in the region. Through the next five days the cold core upper vorticity in the western Atlantic will continuously shrink while cut-off from high-latitude cold air…therefore wind shear will remain low even as the tropical wave enters the eastern Caribbean Sea by day 5. Therefore interests in the Lesser Antilles should monitor this wave as direct impacts will be possible should this wave in fact develop into a tropical cyclone. The forecast track is due west thru day 5 within the deep-layered easterly flow on the south sides of the Atlantic surface ridge and tropical upper ridge. Due to the current position of the tropical wave and latest model consensus…I have once adjusted my forecast track points westward. However some of the models maybe moving the wave too fast to the west while assuming the wave weakens and de-amplifies from the dry air…and lower-amplitude waves in the atmosphere tend to move faster. Therefore I am still not as fast to the west as the model consensus until it is clear the wave won’t develop.

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

IOH 24 Hr Outlook (1800Z Jun 28)...50% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-41W)

IOH 48 Hr Outlook (1800Z Jun 29)...50% chance of tropical cyclone formation (central tropical Atlantic near 13N-47W)

IOH 72 Hr Outlook (1800Z Jun 30)…50% chance of tropical cyclone formation (east of the Lesser Antilles near 13.5N-53W)

IOH 96 Hr Outlook (1800Z Jul 1)…50% chance of tropical cyclone formation (just northeast of Barbados near 14N-59W)

IOH 120 Hr Outlook (1800Z Jul 2)…50% chance of tropical cyclone formation (eastern Caribbean Sea near 15N-65W)


AREA OF INTEREST #2…The surface trough of low pressure in the western Atlantic is en route to coastal Georgia and coastal South Carolina while steered by the Atlantic surface ridge. My update forecast track is nudged north and west due to the current position of the most organized area of thunderstorms located at the northern apex of the surface trough…with the activity supported by split flow upper divergence between two small upper vortices to the west and east also moving in tandem with the surface trough. The NHC has raised development odds to 50% as the thunderstorms have shown signs of organization…same as my previous outlook on this system. ASCAT passes show the north apex of the surface trough is amplified with a near-closed spin and winds at tropical depression force…therefore I have raised my odds of development further to 70%. I have not chosen higher odds or issued a tropical cyclone formation forecast (with intensity forecast points) as the situation is also fragile as indicated by the small size of the thunderstorm region…showing how small the favorable region between the upper vortices is. For instance if the space between the vortices shrinks further or if the surface trough speeds up or slows down a little more than the vortices…that would bring the surface trough into an environment of higher shear and less upper divergence underneath one of the vortices. The fragile environment means that a tropical depression or weak tropical storm is likely the worst case scenario…bringing heavy rainfall and gusty winds with isolated damage potential to coastal Georgia or coastal southern South Carolina tomorrow evening if this scenario happens.

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

IOH 24 Hr Outlook (1800Z Jun 28)...70% chance of tropical cyclone formation (offshore of Georgia near 31N-80W)

IOH 48 Hr Outlook (1800Z Jun 29)...0% chance of tropical cyclone formation (western Georgia near 33.5N-84.5W)

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