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 #75

*******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 10 2021 1:14 AM EDT...

See the area of interest sections below for an update on the trifecta of tropical low pressure systems in the central tropical Atlantic. Please note the following:

(1) The western-most tropical low pressure appears to be developing into a tropical depression or storm as it moves across the Lesser Antilles… and is upgraded to potential tropical cyclone six as a result. See area of interest #3 section below for more details.


A strong tropical wave of low pressure has recently exited Western Africa and is now over the east tropical Atlantic… but has lost its thunderstorm activity due to dry Saharan air to the north. Recently the southern part of the tropical wave has seen an increase in thunderstorms to the south of the Republic of Cabo Verde Islands… will have to see if this trend continues before declaring another area of interest here. And finally… models have also converged on another strong tropical wave emerging from Africa in 5 days… with the models favoring this wave to develop in the long range.


AREA OF INTEREST #1...The tropical wave of low pressure moving across the eastern tropical Atlantic features a large broad cloud swirl centered near 15.5N-37.5W as of 0000Z. The wave has lacked thunderstorms due to dry Saharan air to the north and the cooler far east Atlantic waters north of 15N latitude. However due to the continued cloud swirl structure of the wave… I forecast this wave to still potentially recover once it reaches warmer waters west of 40W longitude as the wave will remain below expansive tropical upper ridging with low shear and upper outflow. This will be especially true at 72+ hours after the northeast Atlantic upper vorticity lingering to the north becomes coaxed on a northeast drift away from the region and ahead of the current eastern upper trough moving across the North Atlantic. I forecast low 10% odds of development by day 5 as there is no model support showing the wave recover… and will adjust the odds up or down depending on if the wave actually recovers or not. By day 5 as the west Atlantic portion of the steering surface ridge potentially weakens a little from a large frontal cyclonic system departing North America… and due to a lingering patch of west Atlantic upper vorticity northeast of the Bahamas… I bend the forecast track a little more towards the north.

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

IOH 24 Hr Outlook (0000Z Aug 10)…0% chance of tropical cyclone formation (central tropical Atlantic near 16N-42.5W)

IOH 48 Hr Outlook (0000Z Aug 11)…0% chance of tropical cyclone formation (central tropical Atlantic near 16.5N-47.5W)

IOH 72 Hr Outlook (0000Z Aug 13)…5% chance of tropical cyclone formation (central tropical Atlantic near 17N-52.5W)

IOH 96 Hr Outlook (0000Z Aug 14)…10% chance of tropical cyclone formation (east of the northern Lesser Antilles near 17.5N-57.5W)

IOH 120 Hr Outlook (0000Z Aug 15)…10% chance of tropical cyclone formation (just north of the northern Lesser Antilles near 19.8N-62.5W)


AREA OF INTEREST #2...The tropical low pressure that has always been trailing to the east-northeast of Area of interest #3 appears to have dissipated over the last 24 hours while ingesting dry Saharan air to the northeast… followed by losing the battle with area of interest #3 which appears to be intensifying into a tropical depression or storm as it steals the surface inflow in the region. This feature has been cancelled from the NHC tropical weather outlook… and this is my final statement on this feature on this blog.


AREA OF INTEREST #3…The tropical low pressure that has been closing in and now crossing the Lesser Antilles has been continuously organizing… and a tropical depression or tropical storm appears to be forming. As a result… the NHC has classified this system as potential tropical cyclone six to allow for the issuance of tropical storm watches and warnings for various islands in the northern Caribbean. I have once again had to adjust the track forecast more north due to the center appearing to consolidate towards the north… and also as area of interest #2 has dissipated which eliminates the possibility of a fujiwhara interaction with that feature. However I am not as far north as the NHC forecast track due to the current more west angle in track I can see in the latest satellite loops. However the track is north enough to allow for possible gusty winds and heavy rains from Dominica and north across the Lesser Antilles for tonight… and across the Virgin Islands and Puerto Rico thru the next 24 hours. The forecast track is expected to curve increasingly north through day 5 as the as a large frontal cyclone over North America is forecast to weaken the west extent of the steering Atlantic surface ridge in the middle of the 5 day forecast period. Even as the frontal cyclone departs and a surface ridge builds over the eastern US… some of the current western Atlantic upper vorticity string is forecast to linger over the eastern Gulf of Mexico which would help bend the track on a north angle as this system will likely be strong/tall enough to be influenced by the upper winds.


Regarding intensity…conditions will be favorable for development over the next five days 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… and so intensification will depend on how much land interaction this system has as it plows through the northern Caribbean. I forecast only gradual intensification over the next 24 hours as this system has been slow to close off a well-defined surface spin. By 48 hours I forecast

a stronger tropical storm as my track keeps it over water… followed by a drop in intensity by 72 hours due to land interaction with Haiti… then another rise in strength while my forecast keeps the center over water just south of Cuba. I only show a slow rise in strength at day 5 due to potential land interaction with western Cuba and also possible western outflow blockage from the lingering east Gulf upper vorticity.


See first paragraph of this area of interest section for potential impacts from the northern Lesser Antilles to Puerto Rico. The following land areas will also have to watch for possible arrival of tropical storm conditions (gusty winds… heavy rain… and coastal sea swells):

**Dominican Republic and Haiti… prepare now as this system will arrive by Wednesday afternoon and evening.

**Jamaica… Cuba… the Cayman Islands… south Florida including the Keys… be aware of this system as it could bring tropical storm conditions in the Thursday to Saturday range across this region.

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

0 Hr Position (0000Z Aug 10)…Tropical low pressure centered over the Lesser Antilles at 15N-60.5W

IOH 24 Hr Forecast (0000Z Aug 11)…40 mph maximum sustained wind tropical storm centered south-southeast of Puerto Rico at 16N-65.5W

IOH 48 Hr Forecast (0000Z Aug 12)…60 mph maximum sustained wind tropical storm centered just south of the Dominican Republic at 17.2N-70.5W

IOH 72 Hr Forecast (0000Z Aug 13)…50 mph maximum sustained wind tropical storm centered between Haiti… Jamaica… and eastern Cuba at 18.5N-75.2W

IOH 96 Hr Forecast (0000Z Aug 14)…65 mph maximin sustained wind tropical storm centered between Cuba and the Cayman Islands at 21N-80W

IOH 120 Hr Forecast (0000Z Aug 15)…70 mph maximin sustained wind tropical storm centered offshore of the northwest Cuba coast at 23N-83W


...COMPUTER MODEL SUMMARY...

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


1200Z CMC Model Run...

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

**For area of interest #2…no tropical cyclone formation shown

**For area of interest #3…surface low develops a closed spin just west of the Lesser Antilles at 24 hours… moves across Puerto Rico and eastern Dominican Republic through 48 hours… moves between Cuba and the Bahamas thru 102 hours…arrives to south Florida at 126 hours… tropical cyclone formation suggested as surface low moves into the northeast Gulf of Mexico at 168 hours.

**Strong tropical wave forecast to emerge from Western Africa at 120 hours… broad low pressure spin of wave crosses the Republic of Cabo Verde Islands at 144 hours… broad low pressure spin centered at 15N-31W at 168 hours.


1200Z ECMWF Model Run...

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

**For area of interest #2…no tropical cyclone formation shown

**For area of interest #3…surface low develops a closed spin just west of the Lesser Antilles at 24 hours…moves across Puerto Rico and eastern Dominican Republic through 48 hours… moves between Cuba and the Bahamas thru 96 hours… arrives to south Florida at 120 hours… tropical cyclone formation suggested on northwest Florida peninsula coast at 144 hours.

**Strong tropical wave forecast to emerge from Western Africa at 120 hours… broad low pressure spin of wave crosses the Republic of Cabo Verde Islands at 144 hours.


1800Z GFS Model Run...

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

**For area of interest #2…no tropical cyclone formation shown

**For area of interest #3…surface low develops a closed spin just west of the Lesser Antilles at 12 hours… passes just south of Puerto Rico at 27 hours… loses closed spin while crossing the Dominican Republic at 39 hours… crosses Cuba thru 105 hours… turns north from western Cuba and regains closed circulation offshore of southwest Florida at 144 hours… tropical cyclone formation suggested near 27.2N-85W at 153 hours.


1200Z NAVGEM Model Run...

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

**For area of interest #2…no tropical cyclone formation shown

**For area of interest #3…no tropical cyclone formation shown

**Strong tropical wave forecast to emerge from Western Africa at 120 hours… broad low pressure spin of wave crosses the Republic of Cabo Verde Islands at 156 hours… tropical cyclone formation suggested west of the islands at 168 hours.

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