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 #91


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


...THURSDAY AUGUST 26 2021 1:48 AM EDT...

URGENT BULLETIN… area of interest #3 has shifted north in track… which results in the following:

**Reduced impacts for Honduras… Nicaragua… Belize… Quintana Roo… Campeche… and Yucatan province. Interests in northern Quintana Roo and Yucatan provinces should still monitor this system as a wobble west in the Forecast track could still bring direct impacts.

**Heavy rains are possible for Jamaica and the Cayman Islands over the next couple of days

**Interests in western Cuba are more likely to see tropical storm to hurricane force conditions in about 60 hours

**Interests along the US Gulf coast near and at Louisiana and Mississippi should be aware of this system… it could approach as a strong hurricane in about 4 days.


See area of interest #1 through #4 sections for updates on all areas being monitored for tropical development in the Atlantic. Elsewhere… a tropical wave is forecast to exit Africa in about 5 days… some models suggest this wave could develop in the eastern tropical Atlantic.


AREA OF INTEREST #1... The large tropical wave of low pressure located in the central Atlantic is currently passing 55W longitude. The wave remains characterized by an elongated north-south circulation. The north part of the elongated circulation continues to be in the process of separating from the rest of the wave as a low pressure spin… located near 27N-55W… while leaning more north in track while gravitated toward the surface ridge weakness induced by area of interest #4 to the west. Satellite imagery over the last several hours revealed a flare up of thunderstorms… and once the thunderstorms pulsed down a better-defined rotation to the northeast has developed near 29N-54W. However this spin is likely mid-level as seen in the CIMSS 850 mb vorticity product (http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=atlantic&sat=wg8&prod=vor&zoom=&time=). Therefore at present we are dealing with a disorganized low pressure area where the surface and mid-level centers are not stacked.


Regarding the track… the low pressure system will soon be turned eastward into a surface ridge weakness to be induced by the divergence zones of the current upper trough and upper vorticity in the northwest Atlantic. The ridge weakness will be maintained by the arrival of the current central Canada upper trough as it amplifies while sliding across the North Atlantic… with a more north angle in track on the east side of the amplified upper trough ensuing by 120 hours.


Although rounds of thunderstorm activity have been aided by divergence on the east side of nearby upper vorticity…. this system remains un-organized as discussed above and so I have lowered development odds overall to a peak of 40% whereas the NHC still retains higher odds. The models have also backed off on developing this system… with the GFS and NAVGEM dropping development and ECMWF and CMC showing a weaker tropical cyclone. In 24 hours the nearby upper vorticity will have retrograded westward out of the way due to the expansion of the west Atlantic upper ridge across the mid-latitudes… with this upper ridging supplying low shear and upper outflow. However with the disorganized state of this system I only have low 15% short-term development odds. An increase in shear is expected by 48 hours as the upper vorticity in the northwest Atlantic nears… with the shear potentially lasting longer through 96 as the GFS suggested the current upper trough from Central Canada taking a longer time to become amplified. However I have kept development odds as high as 40% in case the GFS reverts back to a faster amplifying upper trough (lower shear) scenario that it had yesterday. The lower amplitude trough is also why I have nudged my forecast track more south at the 96 hour window. Despite a more amplified upper trough by 120 hours… I do not raise odds above 40% as the forecast track will be nearing cooler water.

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

IOH 24 Hr Outlook (0000Z Aug 27)… 15% chance of tropical cyclone formation (central Atlantic near 29N-59W)

IOH 48 Hr Outlook (0000Z Aug 28)… 30% chance of tropical cyclone formation (central

Atlantic near 32N-55W)

IOH 72 Hr Outlook (0000Z Aug 29)… 40% chance of tropical cyclone formation (central Atlantic near 32N-49W)

IOH 96 Hr Outlook (0000Z Aug 30)… 40% chance of tropical cyclone formation (central Atlantic near 33N-45W)

IOH 120 Hr Outlook (0000Z Aug 31)… 40% chance of tropical cyclone formation (northeast Atlantic near 36N-39W)


AREA OF INTEREST #2... The tropical wave of low pressure in the eastern Atlantic has seen a decrease in organized thunderstorm activity while ingesting dry Saharan air in the region. Using Satellite animation… the low pressure spin is located near 12.5N-37.5W… or just south of the currently disorganized clumps of thunderstorm activity and also north and west of my previous forecast track. This has required me to adjust the forecast track to the west in the short-term… and due to the recent disorganization of the thunderstorms I have lowered peak odds of development to 40%. This is only a slight lowering and still higher than the NHC outlook as model support showing development has increased.


By days 2 to 4… an upper vortex is forecast to become cut-off from the current Northeast Atlantic upper trough as the current west Atlantic upper ridge expands across the mid-latitudes... placing the vortex just north of this wave. The models suggest tropical cyclone formation enhanced by the eastern divergence zone of the upper vortex. On the other hand the more west position of the tropical wave makes it possible to miss this divergence zone. So as a compromise… I currently forecast the wave to stall its westward travel after 48 hours once the surface ridge weakness associated with area of interest #1 grows…. giving an opportunity for the wave to regenerate northeastward into the eastern divergence zone of the upper vortex. I have low odds of development before the forecast regeneration as this system would be on the higher shear zone on the south side of the upper vortex. I also trim the odds down by 120 hours the upper vortex gets kicked east into this system by the upper trough interacting with area of Interest #1… which would increase the shear over this system once again.

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

IOH 24 Hr Outlook (0000Z Aug 27)… 20% chance of tropical cyclone formation (central tropical Atlantic near 13N-42.5W)

IOH 48 Hr Outlook (0000Z Aug 28)… 30% chance of tropical cyclone formation (central tropical Atlantic near 14N-46W)

IOH 72 Hr Outlook (0000Z Aug 29)… 30% chance of tropical cyclone formation (central tropical Atlantic near 17.5N-44W)

IOH 96 Hr Outlook (0000Z Aug 30)… 40% chance of tropical cyclone formation (central Atlantic near 21N-41W)

IOH 120 Hr Outlook (0000Z Aug 31)… 30% chance of tropical cyclone formation (eastern Atlantic near 25N-37.5W)


AREA OF INTEREST #3... More recent satellite image of the organizing Central Caribbean tropical wave of low pressure taken at 0430Z. The black plus mark is the estimated center of rotation:


A tropical wave of low pressure is currently crossing the central Caribbean Sea with thunderstorm squalls that are enhanced by poleward outflow streaming into the current west Atlantic upper vorticity near the western Bahamas. The thunderstorm squalls have continued to get better organized… and as the upper vorticity collapses while remaining cut-off from high latitude cold air and gets replaced by widespread upper ridging with low shear and upper outflow… upper winds will only get even more favorable for development. As a result… and also due to agreement among models developing this system… I have issued a tropical cyclone formation Forecast as outlined below with the assumption this system will become a tropical cyclone.


The forecast track is shifted north due to where the low pressure spin of the wave is consolidating… and is expected to have a northwest angle while rounding the southwest side of the Atlantic surface ridge. Also the collapsing upper vorticity will likely help guide this system on a north angle over the next 48 hours before dissipating. The track forecast bends more north and then leans east at days 4 and 5 due to the surface ridge weakness of a forecast frontal low passing through southern Canada. I also ramp this system up to a category 2 hurricane in the Gulf of Mexico after 48 hours when the upper vorticity will have dissipated which will allow the upper winds to be optimized for intensification.


See the urgent bulletin at the top of this post for implications regarding impacts with this forecast update.

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

0 Hr Position (0000Z Aug 26)… Tropical low pressure centered south of Jamaica near 15N-76W

IOH 24 Hr Forecast (0000Z Aug 27)… 40 mph maximum sustained wind tropical storm centered south of the Cayman Islands at 16.5N-81W

IOH 48 Hr Forecast (0000Z Aug 28)… 60

mph maximum sustained wind tropical storm centered west of the Cayman Islands at 20N-84W

IOH 72 Hr Forecast (0000Z Aug 29)… 85 mph maximum sustained wind hurricane centered in the Gulf of Mexico at 24.5N-87.5W

IOH 96 Hr Forecast (0000Z Aug 30)… 100 mph maximum sustained wind hurricane centered in the northern Gulf of Mexico at 27.5N-90W

IOH 120 Hr Forecast (0000Z Aug 31)… 95 mph maximum sustained wind hurricane centered over southeastern Mississippi at 31N-89W


AREA OF INTEREST #4…Upper vorticity that has been lingering near the Bahamas through its eastern divergence zone has continued to produce a surface trough of low pressure currently over the central Bahamas. However development is becoming less likely here due to the dominating surface inflow into developing area of interest #3 to the south. This is my final statement on this feature on this blog… note that thunderstorms with heavy rains may spread into south Florida over the next day or so.

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

IOH 24 Hr Outlook (0000Z Aug 27)… 0% chance of tropical cyclone formation (between Cuba and Florida near Bahamas near 24N-80.5W)


...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... surface low pressure becomes better defined near 31.2N-52.5W at 78 hours… tropical cyclone formation near 32N-48.5W at 114 hours.

**For area of interest #2... tropical cyclone formation suggested near 20.1N-46W at 108 hours… located near 22N-46W at 120 hours.

**For area of interest #3... tropical cyclone formation suggested just northwest of western Cuba near 23.8N-85W at 66 hours... makes landfall at hurricane strength at the Texas/Louisiana border at 114 hours.

**For area of interest #4... no development shown

**Strong tropical wave forecast to emerge from Africa at 126 hours... tropical cyclone formation suggested due south of the Republic of Cabo Verde Islands at 144+ hours


1200Z ECMWF Model Run...

**For area of interest #1...Tropical cyclone formation suggested near 32.2N-51W at 72 hours... strong tropical storm strength suggested by 120 hours while passing 37.5N-40W.

**For area of interest #2... tropical cyclone formation suggested near 17.5N-53.5W at 120 hours while curving north in track.

**For area of interest #3... tropical cyclone formation suggested over the western Cayman Islands at 48 hours… passes over the west tip of Cubs just before 72 hours… approaches southwest Louisiana as an intense hurricane by 120 hours

**For area of interest #4... no development shown

**Strong tropical wave forecast to emerge from Africa at 120 hours... rapidly intensifying tropical cyclone formation suggested due south of the Republic of Cabo Verde Islands at 144 hours


1800Z GFS Model Run...

**For area of interest #1... no development shown

**For area of interest #2... tropical cyclone formation suggested near 15N-40W at 42 hours… after turning north weakens to a remnant low near 20.5N-40.5W at 90 hours… remnant low dissipates near 24N-41W at 108 hours

**For area of interest #3... tropical cyclone formation suggested over the western Cayman Islands at 42 hours… passes over the west tip of Cuba at 63 hours and attains compact hurricane status shortly thereafter… makes landfall over southeast Louisiana as an intense hurricane at 105 hours… weakening inland hurricane located over southern Mississippi at 120 hours.

**For area of interest #4... no development shown

**South fragment of tropical wave associated with area of interest #2 forecast to strengthen into a central Caribbean tropical low near 15N-79W at 168 hours


1200Z NAVGEM Model Run...

**For area of interest #1... no development shown

**For area of interest #2... tropical cyclone formation shown near 16N-41W at 84 hours… turns north and reaches 22N-42.5W at 120 hours

**For area of interest #3... tropical cyclone formation shown on south coast of western Cuba near 21N-82.5W at 54 hours… makes landfall over southeast Louisiana as an intense hurricane at 120 hours

**For area of interest #4... no development shown

**Tropical wave emerges from Africa at 54 hours… develops tropical low pressure spin that passes over the Republic of Cabo Verde Islands at 90 hours… tropical low located at 15.5N-29W at 120 hours

** Tropical wave emerges from Africa at 138 hours… tropical cyclone formation suggested over the Republic of Cabo Verde Islands by 168 hours.

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