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 #76

*******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 5:48 PM EDT...

See area of interest #2 section below for an update on Potential Tropical Cyclone Six expected to move across the northern Caribbean islands...and pass near the southeastern Bahamas and south Florida later this week and into the weekend. The tropical wave of low pressure that has recently exited western Africa has become notably better organized at a location further south away from the dry saharan air layer in the region...see area of interest #3 section below for details.


Elsewhere...satellite imagery shows another strong tropical wave with widespread thunderstorms in progress over central Africa which will likely enter the eastern tropical Atlantic over the next couple of days. In addition models have hinted at yet another vigorous wave emerging from western Africa in 4 days. Due to the widespread tropical upper ridging forecast to persist over the eastern tropical Atlantic... a haven of low shear and upper outflow will be present for these waves to also potentially become areas of interest for tropical development in the coming days as long as they stay south of the dry saharan air layer.


AREA OF INTEREST #1...The tropical wave of low pressure that was crossing the eastern tropical Atlantic is now in the central tropical Atlantic passing 41W longitude. Despite the wave beginning to move over warm waters west of 40W longitude and remaining beneath expansive tropical upper ridging with low shear and upper outflow... it has not redeveloped any thunderstorm activity and the definition of its large surface swirl is fading. This could be due to the rapidly developing tropical wave to the southeast (area of interest #3) stealing the surface inflow in the region. Therefore I have dropped my odds of this wave developing down the road ot 0%... and this is my final statement on this tropical wave on this blog.

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

IOH 24 Hr Outlook (1800Z Aug 11)...0% chance of tropical cyclone formation (central tropical Atlantic near 15N-46W)


AREA OF INTEREST #2...The tropical low pressure that has been crossing the northern Lesser Antilles and northeastern Caribbean Sea waters due south of the Virgin Islands and Puerto Rico has been continuously organizing...and now has an impressive deck of thunderstorms organized in a large swirl. Beneath this deck however the NHC aircraft reconnaissance has not been able to locate a well-defined surface circulation...and so this system continues to be designated as potential tropical cyclone six as a tropical depression or storm could quickly form... to allow for the ongoing issuance of tropical storm watches and warnings for islands across the north Caribbean and southeastern Bahamas in the path of this system. Based on the latest position of this system...I have once again nudged my forecast track north... but remain south of the NHC forecast track and model consensus as satellite loops show a more west angle in track ongoing. The forecast track is expected to curve increasingly north over the next five days 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 in the near-term 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 region. My intensity forecast still shows 60 mph maximum sustained winds for tomorrow and before landfall with the Dominican Republic south coast given the impressive and organized thunderstorm cloud deck this system has on satellite pictures which could allow for brisk strengthening once a well-defined surface spin commences. I have lowered my intensity forecast for the middle part of the forecast period (48 and 72 hours) as my updated forecast track keeps the center over the Dominican Republic...Haiti...and then only after a short time over water the track moves the center across much of Cuba. I do not drop the intensity forecast below 45 mph max sustained winds however as only a small shift in track would allow the center to take advantage of water offshore of either side of Cuba... or alternatively the offshore thunderstorm bands could continue to produce tropical storm force winds even as the center moves through Cuba. I show a slightly higher intensity of 50 mph max sustained winds by 96 hours as the center moves over water...but show minimal strengthening due to potential disruption from the lingering eastern Gulf upper vorticity. Even though my forecast track at 120 hours moves this system across the Florida peninsula...I maintain a forecast strength of 40 mph max sustained winds as I currently forecast this system to transition into a more subtropical type of storm aided by the eastern divergence zone of the upper vorticity...resulting in a potentially larger broader storm producing max winds along coastal Florida even with the center over land.

The following land areas will have to watch for arrival of tropical storm conditions (gusty winds... heavy rain with flash flood potential... and coastal sea swells) in the coming days:

**Puerto Rico and the Virgin Islands will experience heavy rainfall and gusty winds over the next few hours. Based on the US National Weather Service Station data at weather.gov... Ponce on the south coast of Puerto Rico has reported wind gusts as high as 29 mph... and St Thomas (King Airport) in the US Virgin Islands has reported gusts as high as 28 mph.

**Dominican Republic and Haiti... preparations should be finished by tomorrow morning as conditions will deteriorate soon after.

**Based on the latest forecast track... the potential for tropical storm conditions is reducing for Jamaica and the Cayman Islands...although coastal sea swells cannot be ruled out by Thursday and Friday.

**I recommend interests in Cuba begin preparing for tropical storm conditions to arrive by Thursday and Friday

**Interests in the southeast Bahamas are under a tropical storm watch. It is possible that the center stays south of the islands... but in this scenario the northern rain bands may still bring heavy rainfall. However I recommend interests here should prepare for possible tropical storm conditions to arrive by Thursday in the event this system redevelops a new center on the north coast of the Dominican Republic or Haiti after tomorrow's landfall which would bring the center closer to the area.

**Interests across the Florida peninsula and Keys should be aware of this system as it could bring tropical storm conditions in the region this weekend.

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

0 Hr Position (1800Z Aug 10)...Tropical low pressure centered south of the Virgin Islands at 16.5N-65W

IOH 24 Hr Forecast (1800Z Aug 11)...60 mph maximum sustained wind tropical storm centered just south of the Dominican Republic at 18N-70W

IOH 48 Hr Forecast (1800Z Aug 12)...45 mph maximum sustained wind tropical storm centered between Haiti and eastern Cuba at 19N-74.8W

IOH 72 Hr Forecast (1800Z Aug 13)...45 mph maximum sustained wind tropical storm centered over central Cuba at 22N-79W

IOH 96 Hr Forecast (1800Z Aug 14)...50 mph maximum sustained wind tropical storm centered over the eastern Florida Keys at 24.5N-81W

IOH 120 Hr Forecast (1800Z Aug 15)...40 mph maximum sustained wind tropical storm centered over the central Florida peninsula at 27.5N-81.5W


AREA OF INTEREST #3...The strong tropical wave of low pressure that has recently entered the eastern tropical Atlantic has continued to see organized thunderstorm activity on its south side... located away from the dry saharan air and cooler far east Atlantic waters. In fact this thunderstorm activity has rapidly organized over the last 24 hours into a concentrated low pressure spin currently centered at 12N-27.5W... and the NHC has added this tropical wave as an area of interest in their tropical weather outlook. Given the wave's already-impressive organization...I have gone higher than the NHC outlook as of this writing and forecast 60% odds of tropical cyclone formation by day 5. I have not gone any higher at this time to see if the tropical wave maintains its organization... or to see if models come on board and develop this system. It is curious the models don't develop this wave despite its current organization...and favorable conditions of warm waters... low shear and upper outflow beneath expansive upper ridging as the wave plows west through the tropical Atlantic under the guidance of widespread Atlantic surface ridging. Perhaps the models have not yet been initialize with the currently organized structure of the wave.

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

IOH 24 Hr Outlook (1800Z Aug 11)...50% chance of tropical cyclone formation (eastern tropical Atlantic near 12.5N-32.5W)

IOH 48 Hr Outlook (1800Z Aug 12)...50% chance of tropical cyclone formation (eastern tropical Atlantic near 13N-37.5W)

IOH 72 Hr Outlook (1800Z Aug 13)...60% chance of tropical cyclone formation (central tropical Atlantic near 13.5N-42.5W)

IOH 96 Hr Outlook (1800Z Aug 14)...60% chance of tropical cyclone formation (central tropical Atlantic near 14N-47.5W)

IOH 120 Hr Outlook (1800Z Aug 15)...60% chance of tropical cyclone formation (central tropical Atlantic near 14.5N-52.5W)


...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...surface low develops a closed spin between southwest Puerto Rico and southeastern Dominican Republic at 18 hours...while moving across Haiti and the Dominican Republic through 30 hours loses closed circulation... redevelops closed circuation just offshore of the north Haiti coast at 42 hours... passes between Cuba and the Bahamas through 78 hours... tropical cyclone formation suggested by 90 hours as system moves west-northwest across Florida Keys... strengthens at 96 hours while centered on the southwest Florida peninsula coast... strong tropical storm status suggested over the eastern Gulf of Mexico by 126 hours while located at 28N-85W...

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


1200Z ECMWF Model Run...

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

**For area of interest #2...surface low makes landfall over the eastern Dominican Republic at 24 hours... after emerging from northwest Haiti by 48 hours the surface low is disorganized without a closed spin... the recovering surface low passes between Cuba and the Bahamas through 72 hours and then the Florida Keys at 96 hours... tropical cyclone formation suggested by 120 hours while surface low turns north across the eastern Gulf of Mexico and reaches 27.5N-84W

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

**Strong tropical wave forecast to emerge from Western Africa at 96 hours... develops a broad and weak low pressure spin near 12.5N-30W at 144 hours.


1200Z GFS Model Run...

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

**For area of interest #2...compact tropical cyclone formation suggested just south of the Virgin Islands at 6 hours... weakens to a compact remnant low as it approaches landfall over the eastern Dominican Republic at 21 hours... remnant low emerged from north Haiti coast at 39 hours... weakens to a remnant trough while passing between Cuba and the Bahamas through 87 hours... surface trough regenerates into a compact tropical cyclone centered just offshore of southeast Florida at 102 hours... due to landfall across south Florida weakens to a remnant low while reaching the southwest Florida coast at 114 hours... remnant low regenerates into a tropical cyclone in the northeast Gulf of Mexico and just offshore of the Florida panhandle big bend coast at 135 hours.

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

**Strong tropical wave forecast to emerge from Western Africa at 111 hours... broad low pressure spin of tropical wave passes over the Republic of Cabo Verde Islands at 138 hours... center of broad spin located at 13N-36W at 168 hours.


0600Z NAVGEM Model Run...

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

**For area of interest #2...tropical cyclone formation suggested just south of the Virgin Islands at 12 hours... center passes between Puerto Rico and the Dominican Republic at 24 hours... then offshore of the Dominican Republic north coast through 42 hours... strengthens over the southeastern Bahamas at 54 hours... reaches hurricane strength just southwest of Andros Island of the western Bahamas at 78 hours... makes landfall over south Florida at 96 hours as an intense hurricane... center of intense hurricane located in the eastern Gulf of Mexico near 28N-84W at 120 hours.

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

**Strong tropical wave forecast to emerge from Western Africa at 150 hours...quick tropical cyclone formation suggested just offshore of west Africa near 17.5N-18W at 168 hours.

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