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 #72 (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 4:27 AM EDT...

Satellite image as of 1810Z 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 1800Z:

GFS Model Upper-Level Winds 1800Z:

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 by the NHC for possible development in the coming days.


AREA OF INTEREST #1...More recent infrared satellite image of all three areas of interest as of 0710Z…the center or rotation for each feature is marked with a yellow plus:

The vigorous tropical wave of low pressure moving across the eastern tropical Atlantic has spent Friday and now passing south of the Republic of Cabo Verde Islands while absorbing what was left of the previous disturbance Invest 91-L west of the islands. While the low-level cloud swirl (centered near 12.5N-26W at 0000Z) and thunderstorm bands have become better defined over time…the intensity of the thunderstorm bands has also relaxed and the size of the circulation appears to have grown markedly larger during the absorption process. My updated forecast track below is nudged southward over my previous as this system has also stayed further south during the absorption process. While it may seem like a good idea to raise development odds above 50% as the forecast track is further away from the dry Saharan air to the north…I have kept them at 50% by day 5 as the enlarged size of this system makes it more challenging for a tropical cyclone to consolidate within…and there is no telling if this system gets even larger and less organized as it appears to be poised to also absorb area of interest #2. Of note…some of the upper vorticity currently in the east Atlantic may retrograde southwest around the North Atlantic upper ridge and potentially interfere with the northern outflow of this system by day 4 which is why I only slowly ramp development odds upward between days 3 and 4. However by day 5 the upper vorticity is forecast to retreat away from this system while coaxed on a northeast drift ahead of the current central North America upper trough as that trough moves across the North Atlantic…and so this is when I ramp up odds faster and into the 50% mark.

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

IOH 24 Hr Outlook (0000Z Aug 8)…5% chance of tropical cyclone formation (eastern tropical Atlantic near 13N-31W)

IOH 48 Hr Outlook (0000Z Aug 9)…10% chance of tropical cyclone formation (eastern tropical Atlantic near 13.5N-36W)

IOH 72 Hr Outlook (0000Z Aug 10)…30% chance of tropical cyclone formation (central tropical Atlantic near 14N-41W)

IOH 96 Hr Outlook (0000Z Aug 11)…35% chance of tropical cyclone formation (central tropical Atlantic near 14.5N-46W)

IOH 120 Hr Outlook (0000Z Aug 12)…50% chance of tropical cyclone formation (central tropical Atlantic near 15N-51W)


AREA OF INTEREST #2...The rather large tropical wave of low pressure that has been moving through the central tropical Atlantic currently has its axis passing 55W longitude has left behind its low pressure swirl at 40W longitude…which has been stationary near 14N-40W over the last several hours. This indicates the enlarged circulation of area of interest #1 is tugging at this low pressure swirl and may even cause it to drift south over the next 24 hours. I have drastically dropped development odds of this feature to 0% over my previous update as it now appears to be in a holding pattern waiting to be absorbed by area of interest #1. I plan this to be my final statement on this low pressure swirl…unless it continues to be mentioned in the NHC tropical weather outlook by my next update.

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

IOH 24 Hr Outlook (0000Z Aug 8)…0% chance of tropical cyclone formation (central tropical Atlantic near 13N-40W)


AREA OF INTEREST #3…The rather large tropical wave of low pressure that has been moving through the central tropical Atlantic currently has its axis passing 55W longitude…and appears to have left behind yet another low pressure swirl near 13N-49W. This swirl has recently been introduced into the NHC tropical weather outlook since 8 PM EDT….and is fairly weak thus far with some scattered thunderstorms nearby and mainly to the south. Despite this feature being beneath expansive tropical upper ridging with low shear and upper outflow through the next five days while it moves west across the Lesser Antilles and into eastern Caribbean Sea while steered by the expansive Atlantic surface ridge… none of the model runs through 18Z want to develop this system. Perhaps this is due to the models seeing this system competing for low-level inflow with areas of interest #1 and #2 to the east…especially as they potentially congeal into one rather large circulation? Either way…with the current lack of model support and current disorganized thunderstorm activity…I agree with the NHC’s low 10% odds of development. Because the odds of development are currently low… there is no guarantee of notable impacts to the Lesser Antilles at this time as this low pressure area potentially moves through the islands in 48 to 72 hours. Note the initial forecast track for the next 24 hours in my outlook below is west-southwest due to the potential of fujiwhara interaction with areas of interest #1 and #2 to the east…followed by a steady west to west-northwest track around the Atlantic surface ridge through days 2 through 5.

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

IOH 24 Hr Outlook (0000Z Aug 8)…0% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-53W)

IOH 48 Hr Outlook (0000Z Aug 9)…10% chance of tropical cyclone formation (east of the Lesser Antilles near 13N-58W)

IOH 72 Hr Outlook (0000Z Aug 10)…10% chance of tropical cyclone formation (eastern Caribbean Sea just west of the Lesser Antilles near 13.5N-62W)

IOH 96 Hr Outlook (0000Z Aug 11)…10% chance of tropical cyclone formation (eastern Caribbean Sea near 14N-66W)

IOH 120 Hr Outlook (0000Z Aug 11)…10% chance of tropical cyclone formation (central Caribbean Sea near 14.5N-70W)


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