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 #73 (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.**********


...SATURDAY AUGUST 7 2021 11:59 PM EDT...

Satellite image as of 1820Z before tonight’s sunset across the Atlantic. 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:

See the area of interest sections below for the current trifecta of tropical low pressure systems in the central and eastern tropical Atlantic being monitored for possible development in the coming days. Please note the following:

(1) The tropical low pressure currently at 51W longitude has seen an increase in organizing thunderstorms…and will be crossing the Lesser Antilles in 48 hours. Interests here should pay attention to this system…see area of interest #3 section for details

(2) The tropical low pressure currently at 40.5W longitude may cross the northern Lesser Antilles… Virgin Islands…and Puerto Rico in 4 to 5 days. Interests here should monitor the progress of this system…see area of interest #2 section for details


Elsewhere…another strong tropical wave of low pressure is in progress over Central Africa

with a widespread thunderstorm mass. This tropical wave may become yet another area of interest as it emerges into the eastern tropical Atlantic in a couple of days or so as the expansive tropical Atlantic upper ridge with low shear and upper outflow is expected to persist.


AREA OF INTEREST #1...The large spin of the vigorous tropical wave of low pressure moving across the eastern tropical Atlantic has consolidated to the east…resulting in a smaller rotation just southwest of the Republic of Cabo Verde Islands that had an increase in thunderstorm activity…but as we move through the nighttime hours the thunderstorms have collapsed. The east consolidation of this system has caused me to shift the forecast track points east…and also to the north as this system is also further north than yesterday. The more north position…and also the lack of a westward travel today….might be due to fujiwhara interaction with area of interest #2 to the west…but the most recent satellite animation suggests that all three areas of interest are starting to finally move west in tandem perhaps as all three areas have become more consolidated to allow for reduced fujiwhara interactions between them. So the forecast track below is a gradual acceleration to a typical 5W longitude per day westward speed over the next 24 hours…followed by maintenance of that speed through day 5. A slight increase in the north angle in track is show between 72 and 96 hours as some of the upper vorticity currently in the northeast Atlantic will retrograde southwest around the North Atlantic upper ridge and potentially try to pull the track of this system more north…especially if this system develops a stronger/taller structure that could allow for more interaction with the upper vorticity. By day 5…the upper vorticity is forecast to retreat away from this system while coaxed on a northeast drift ahead of the current eastern North America upper trough as that trough moves across the North Atlantic…and so I reduce the north angle in track by that time.


I have dropped odds of development to 30% by day 5 due to the recent decline in thunderstorms…perhaps brought on by dry Saharan air to the north and also the cooler far east Atlantic waters north of 15N latitude. I only slowly ramp up the odds in the short-term…and ramp up the odds a little faster in the long term once this system moves toward warmer water.

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

IOH 24 Hr Outlook (1800Z Aug 8)…5% chance of tropical cyclone formation (eastern tropical Atlantic near 15N-29W)

IOH 48 Hr Outlook (1800Z Aug 9)…5% chance of tropical cyclone formation (central tropical Atlantic near 15.5N-34W)

IOH 72 Hr Outlook (1800Z Aug 10)…10% chance of tropical cyclone formation (eastern tropical Atlantic near 16N-39W)

IOH 96 Hr Outlook (1800Z Aug 11)…20% chance of tropical cyclone formation (central tropical Atlantic near 17N-44W)

IOH 120 Hr Outlook (1800Z Aug 12)…30% chance of tropical cyclone formation (central tropical Atlantic near 17.5N-49W)


AREA OF INTEREST #2...The tropical low pressure at 40W longitude that has been generally stationary due to the tug of area of interest #1 to the east has just begun to finally drift west. This could be due to the consolidation of area of interest #1 at a location further away which means that area of interest #1 has less of a grip on this tropical low pressure of interest. This also means the tropical low pressure has a new lease on life as it avoids absorption into area of interest #1…and therefore I have had to create a five day Outlook on this system as outlined below. The forecast track below is a gradual acceleration from the current position at 14.5N-40.5W to a typical 5W longitude per day westward speed over the next 24 hours…followed by maintenance of that speed through day 5.


Although thunderstorm activity has increased recently…it is displaced well southwest of the swirl center and therefore I only have low 30% odds of development by day 5…the same as what I assigned for area of interest #1. However my short-term odds ramp up slightly faster than area of interest #1 due to this system being over warmer water. This system may cross the northern Lesser Antilles… Virgin Islands…and Puerto Rico in 4 to 5 days. Interests here should monitor the progress of this system in case it does develop further…which is a possibility as the west Atlantic upper vorticity string is forecast to weaken which will allow for tropical upper ridging with low shear and upper outflow to stay over this system thru day 5.

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

IOH 24 Hr Outlook (1800Z Aug 8)…5% chance of tropical cyclone formation (central tropical Atlantic near 15N-43.5W)

IOH 48 Hr Outlook (1800Z Aug 9)…10% chance of tropical cyclone formation (central tropical Atlantic near 15.5N-48.5W)

IOH 72 Hr Outlook (1800Z Aug 10)…15% chance of tropical cyclone formation (east of the Lesser Antilles near 16N-53.5W)

IOH 96 Hr Outlook (1800Z Aug 11)…20% chance of tropical cyclone formation (just east of the northern Lesser Antilles near 16.5N-58.5W)

IOH 120 Hr Outlook (1800Z Aug 12)…30% chance of tropical cyclone formation (northeast Caribbean Sea near 17N-63.5W)


AREA OF INTEREST #3…More recent satellite

image of the tropical low pressure area near 50W longitude as of 0250Z…red plus marks estimated center of rotation:

The tropical low pressure near 50W longitude over the last 24 hours as seen a gradual increase in organizing thunderstorms over and southeast of the center of rotation. This feature has been moving more slowly west than I previously forecast…perhaps from the tug of area of interest #2 to the east. The most recent satellite animation suggests that all three areas of interest are starting to finally move west in tandem perhaps as all three areas have become more consolidated to allow for reduced interactions between them. So the forecast track below is a gradual acceleration from the current position near 13N-51W to a typical 5W longitude per day westward speed over the next 24 hours…followed by maintenance of that speed through day 5. I currently forecast no north angle in the track through day 4 as the close proximity of area of interest #2 may still allow for some slight fujiwhara influence. I do finally show some slight north angle in the track by day 5 however as a large frontal cyclonic system forecast to be over North America may weaken the west extent of the steering Atlantic surface ridge.


Due to the increase in organized thunderstorm activity…I have raised odds of development to 40% by day 5. This system is expected to cross the Lesser Antilles in 48 hours. Interests here should monitor the progress of this system in case it does develop further in the short-term… which may require a quick preparation for heavy rains and gusty winds for some of the islands before the system arrives. Short-term and also longer term development in the Caribbean is a possibility as the west Atlantic upper vorticity string is forecast to weaken which will allow for tropical upper ridging with low shear and upper outflow to stay over this system thru day 5.

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

IOH 24 Hr Outlook (1800Z Aug 8)…10% chance of tropical cyclone formation (east of the Lesser Antilles near 13N-54W)

IOH 48 Hr Outlook (1800Z Aug 9)…20% chance of tropical cyclone formation (just east of the Lesser Antilles near 13N-59W)

IOH 72 Hr Outlook (1800Z Aug 10)…30% chance of tropical cyclone formation (eastern Caribbean Sea near 13N-64W)

IOH 96 Hr Outlook (1800Z Aug 11)…40% chance of tropical cyclone formation (central Caribbean Sea near 13N-69W)

IOH 120 Hr Outlook (1800Z Aug 12)…40% chance of tropical cyclone formation (central Caribbean Sea near 14N-74W)


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