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 #68

Updated: Aug 4

*******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.**********


...TUESDAY AUGUST 3 2021 6:20 AM EDT...

Satellite image as of 1000Z today. 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 Aug 2:

GFS Model Upper-Level Winds 1800Z Aug 2:

See the pair of area of interest sections below for new areas of interest in the Atlantic tropics which include:

(1) area of interest #1…surface trough of low pressure south-southwest of the Republic of Cabo Verde Islands

(2) area of interest #2…surface low pressure area along a frontal boundary offshore of the southeastern United States.


Elsewhere…another vigorous tropical wave of low pressure is forecast to emerge from the west coast of Africa in about three to four days …and has potential to develop per the latest GFS and ECMWF model runs with the support of low shear and upper outflow beneath the eastern tropical Atlantic upper ridge forecast to persist over the next several days.


AREA OF INTEREST #1…As of 2 PM EDT yesterday afternoon…the NHC has initiated an area of interest in their tropical weather outlook in the eastern tropical Atlantic at a location south-southwest of the Republic of Cabo Verde Islands in the eastern Atlantic. The feature is a surface trough of low pressure on the east side of a large scale tropical wave that has moved from 20W to 30W longitude over the last day…and based on the most recent satellite imagery the surface trough is currently located near 11N-26W and moving northwest while steered by the east side of the large scale wave while having an axis of scattered showers and thunderstorms. On this track…the surface trough should stay just west of the islands in the next 24 hours…then turn more west by 48 hours while running into the south end of the Atlantic surface ridge. I only forecast a very low 5% odds of development in the short-term as the surface trough is not producing organized thunderstorms and is already heading toward dry Saharan air…and then forecast 0% odds of development by 48 hours as the surface trough becomes fully embedded in the dry air. The models seem to also agree that this feature will weaken in the dry Saharan air by 48+ hours.

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

IOH 24 Hr Outlook (0600Z Aug 4)…5% chance of tropical cyclone formation (just southwest of the Republic of Cabo Verde Islands near 14N-27.5W)

IOH 48 Hr Outlook (0600Z Aug 5)…0% chance of tropical cyclone formation (eastern tropical Atlantic near 16N-29W)


AREA OF INTEREST #2…The stalled surface frontal boundary offshore of the eastern US has become recently re-enforced as another cold front that was inland has moved offshore with the push of the upper trough currently over eastern North America. Based on the satellite imagery overnight…a surface low pressure area just offshore of the southeastern US appears to be gradually forming near 30.5N-80.2W along the front’s tail end…with thunderstorms over north Florida on its west side. Models (except the ECMWF) agree that this surface low pressure will strengthen and become more defined with the support of the eastern divergence zone of the aforementioned upper trough and also the outflow on the west side of the western Atlantic upper ridge. The outflow and low shear of the upper ridge could allow for tropical development as the surface low slides along or just offshore of the US east coast over the next day or so due to the deep-layer southerly flow between the upper trough and upper ridge and west side of the Atlantic surface ridge whose strength will keep the surface low pressure close to shore. The NAVGEM explicitly shows tropical development…the CMC seems to suggest it as well with a circular structure to the surface low…while its a close call on the GFS which shows an initially elongated low that becomes more circular. With the model support…I have chosen to keep odds of development slightly above 10%…at 15%…and will wait to see if thunderstorms increase before raising odds of development further. I drop odds of development to 0% by 72 hours as the surface low moves into cooler waters and sheds whatever tropical characteristics it may obtain.


From now through Friday expect:

**Heavy rainfall with flash flooding potential from north Florida all the way up the US east coast to Maine regardless of tropical development. As of this writing…a flash flood watch is in effect for parts of this region.

**The potential for gusty winds and coastal

surf from the coastal Carolinas to coastal Maine…at first from possible tropical development in the short-term and then possible support from the upper trough by non-tropical means after this system moves into cooler water.

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

IOH 24 Hr Outlook (0600Z Aug 4)…15% chance of tropical cyclone formation (Cape Fear North Carolina near 33.8N-77.8W)

IOH 48 Hr Outlook (0600Z Aug 5)…15% chance of tropical cyclone formation (offshore of Maryland and Delaware near 37.8N-74W)

IOH 72 Hr Outlook (0600Z Aug 6)…0% chance of tropical cyclone formation (just offshore of Maine near 43.5N-67.7W)


...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)


0000Z CMC Model Run...

**For area of interest #1…no tropical cyclone formation shown

**For area of interest #2…small circular low pressure forms along front and just offshore of Cape Hatteras North Carolina near 35.2N-75W at 36 hours…becomes more elongated (less tropical and more frontal) in nature over cooler water offshore of Cape Cod Massachusetts near 40N-70.5W at 54 hours….remnant low makes landfall over Nova Scotia at 66 hours while weakening to a surface trough.


1200Z Aug 2 ECMWF Model Run (0000Z run unavailable at above-mentioned source)…

**For area of interest #1…low pressure becomes defined on east side of the current wave at 30W longitude at a location just south-southwest of the Republic of Cabo Verde Islands at 24 hours…low pressure pushed north-northwest into the southwestern islands by the wave and weakens to a surface trough by 48 hours.

**For area of interest #2…No defined low pressure forms along surface front

**Vigorous tropical wave of low pressure forecast to emerge from west Africa at 96 hours…develops broad low pressure spin south of the Republic of Cabo Verde Islands at 120 hours…however the low pressure spin begins to weaken by 144 hours as the wave passes 30W longitude.

0000Z GFS Model Run...

**For area of interest #1…low pressure becomes defined on east side of the current wave at 30W longitude at a location just south of the Republic of Cabo Verde Islands at 9 hours…low pressure pushed north-northwest into the islands by the wave thru 33 hours…weakens to a surface trough just northwest of the islands by 51 hours

**For area of interest #2…elongated non-tropical low forms along front and offshore of Maryland and Delaware near 37.8N-74W at 57 hours…moves across Cape Cod Massachusetts with a more circular and compact structure by 69 hours…makes landfall at the Maine/Canada border at 78 hours while weakening to a surface trough shortly thereafter

**Vigorous tropical wave of low pressure forecast to emerge from west Africa at 72 hours…compact tropical cyclone formation suggested just south of the Republic of Cabo Verde Islands at 102 hours near 11.5N-22.8W…tropical cyclone positioned just southwest of the islands at 120 hours.

0000Z NAVGEM Model Run...

**For area of interest #1…low pressure becomes defined on east side of the current wave at 30W longitude at a location just southeast of the Republic of Cabo Verde Islands at 18 hours…low pressure pushed north-northwest into the northern islands by the wave thru 42 hours…turns more west in track and weakens to a surface trough just northwest of the islands by 66 hours

**For area of interest #2…elongated non-tropical low forms along front and just offshore of the Carolinas near 32.5N-78W at 30 hours…tropical cyclone formation suggested as the low pressure moves across the Outer Banks of North Carolina at 42 hours…cyclone center moves across Cape Cod Massachusetts between 60 and 66 hours…makes landfall in Maine by 72 hours while weakening to a remnant low

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