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 #92

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


...FRIDAY AUGUST 27 2021 1:00 AM EDT...


See Ida section below for the latest on the new tropical storm which has formed in the western Caribbean. See area of interest #1 through #3 sections for updates on all other areas being monitored for tropical development in the Atlantic.


TROPICAL STORM IDA... More recent satellite image of Tropical Storm Ida as of 0330Z. Black plus marks the location of the surface center:

While passing just southwest of Jamaica…the lowest pressure center of the vigorous central Caribbean tropical wave proceeded to intensify into tropical depression nine and then Tropical Storm Ida this past afternoon. The continuous development process has been aided by poleward outflow streaming into the nearby upper vorticity to the northwest. Satellite imagery has shown the surface center of Ida has been toward the southwest side of the strongest and most organized thunderstorm squalls… an effect of light shear imparted by the aforementioned upper vorticity. Given the current more north position of Ida compared to my previous forecast and that the surface center isn’t mature yet and could regenerate northeast into the more organized thunderstorm squalls… I have opted to shift the forecast track more north and east. The forecast track is expected to have a northwest angle while rounding the southwest side of the Atlantic surface ridge. The track forecast bends more north and then leans east at days 3 to 5 due to the surface ridge weakness of a forecast frontal low passing through southeastern Canada. I also ramp this system up to a category 2 hurricane after 24 hours when the upper vorticity will have dissipated while remaining cut-off from high-latitude cold air… which will allow the upper winds to be optimized for intensification as widespread upper ridging with low shear and upper outflow will be in place in the wake of the upper vorticity.


With these forecast updates… the following impacts are expected:

**Interests in Nicaragua… Honduras… Belize…and the Mexican provinces of Quintana Roo… Yucatan… and Campeche… are not expected to see direct impacts from Ida. However coastal sea swells are possible from Ida should it quickly strengthen in the short-term.

**Heavy rainfall with flash flooding potential is expected to continue across Jamaica, and will spread across the Cayman Islands and Cuba over the next 24 hours. Coastal sea swells are also expected. The Cayman Islands are currently under a tropical storm warning as gusty winds are expected… and are likely to occur now as the center of the storm is nearing. Per the home page bulletins of this site… interests in western Cuba area also under a tropical storm warning and should continue preparing for possible tropical storm to hurricane force conditions to arrive by late tomorrow (Friday).

**Interests in the Florida Keys could see some gusty winds… coastal sea swells… and heavy rain tomorrow night and early Saturday from the outer northeast bands of Ida as the forecast track has shifted east closer to the region.

**Interests across the United States Gulf coast in the hurricane and tropical storm watch region across Louisiana… Mississippi… and Alabama should begin to prepare for what is forecast to be a strong hurricane Ida. Preparations should include a plan for evacuating to higher ground further inland if you live in an area prone to coastal storm surge flooding… and accounting for the expectation of damaging winds with widespread power outages. Ida is expected to be upon the region by late Sunday.

**As Ida will take time to weaken inland after landfall… tropical storm force winds with some damage potential could spread inland across southeast Louisiana… southern Mississippi… and southwestern Alabama late Sunday and into Monday… begin preparing now.

**Coastal sea swells will be possible for the Florida panhandle coast late this weekend where the east side of a strong hurricane Ida will tend to push water toward shore well away from the center of circulation.

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

0 Hr Position (0000Z Aug 27)… 40 mph maximum sustained wind tropical storm centered just south of the Cayman Islands at 18N-80.1W

IOH 24 Hr Forecast (0000Z Aug 28)… 60

mph maximum sustained wind tropical storm centered over western Cuba at 22.6N-82.5W

IOH 48 Hr Forecast (0000Z Aug 29)… 85 mph maximum sustained wind hurricane centered in the Gulf of Mexico at 27N-86W

IOH 72 Hr Forecast (0000Z Aug 30)… 100 mph maximum sustained wind hurricane centered over the southeast corner of Mississippi at 30.5N-88.8W

IOH 96 Hr Forecast (0000Z Aug 31)… Remnant low centered over the northwest corner of Alabama at 34.5N-87.8W


AREA OF INTEREST #1... The surface low pressure area in the open central Atlantic that originated from the north fracture of a tropical wave has become better organized while the surface and mid-level centers have become stacked near 31N-55W with thunderstorms organizing around the stacked circulation. Regarding the future track of this system… a turn to the east is expected while falling into a surface ridge weakness induced by the divergence zone of the current northwest Atlantic upper vorticity. 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 96 hours. The forecast track points have been adjusted north and east to account for the current position of the system relative to the previous forecast.


I have raised short-term development odds to 50% due to the increased organization… and not higher as all models except the ECMWF have dropped showing development. Also the wind shear is expected to increase at 24+ hours as the upper vorticity in the northwest Atlantic nears… with the shear through 72 as the current upper trough from Central Canada is still forecast to take a longer time to become amplified. Therefore my long term development odds are slightly lowered compared to before as the shear forecast has remained negative. Despite a more amplified upper trough with lower shear and a healthy eastern divergence zone by 96 hours… I drop development odds to 0% as the forecast position is over cooler northeast Atlantic waters.

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

IOH 24 Hr Outlook (0000Z Aug 28)… 50% chance of tropical cyclone formation (central

Atlantic near 33N-52W)

IOH 48 Hr Outlook (0000Z Aug 29)… 35% chance of tropical cyclone formation (central Atlantic near 33N-47.5W)

IOH 72 Hr Outlook (0000Z Aug 30)… 35% chance of tropical cyclone formation (central Atlantic near 35N-42.5W)

IOH 96 Hr Outlook (0000Z Aug 31)… 0% chance of tropical cyclone formation (northeast Atlantic near 37.5N-37.5W)


AREA OF INTEREST #2... The tropical wave of low pressure now in the central Atlantic has become considerably better organized with banding features reminiscent of a tropical depression. Using Satellite animation… the low pressure spin is located near 12.5N-42.5W. I have raised short term development odds to 90% given these events.


After 24 hours… an upper vortex is forecast to become cut-off from the current Northeast Atlantic upper vorticity string due to the strength of the current central Atlantic upper ridge. The vortex is expected to be just north of this wave. Due to the more west track this system has taken… the models suggest what I had forecasted yesterday… which is to stall the wave’s westward travel after 24 hours once the surface ridge weakness associated with area of interest #1 grows…. giving an opportunity for the wave to relocate northeastward into the supportive eastern divergence zone of the upper vortex. Given the upper vortex will somewhat increase the shear… I drop development odds to 60% in the medium-term. Odds are kicked down further to 30% by day 4 (96 hours) as 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 further. Although the shear may reduce at 120 hours once the upper trough passes… this system may end up beneath the western convergence zone of the upper trough which will tend to increase surface pressure as evidenced by the upper trough creating a new northeast Atlantic surface ridge in the modeling by 120 hours which will sandwich this system between that ridge and the eastern cell of the Atlantic surface ridge. With a possible rise in surface pressure… I do not raise development odds above the 30% despite possible lower shear. On a final note… my day 4 and day 5 forecast positions are nudged west due to the latest forecast strength of the eastern cell of the Atlantic surface ridge which will be supported by the west convergence zone of the current northeast Atlantic upper vorticity string.

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

IOH 24 Hr Outlook (0000Z Aug 28)… 90% chance of tropical cyclone formation (central tropical Atlantic near 13.5N-46W)

IOH 48 Hr Outlook (0000Z Aug 29)… 60% chance of tropical cyclone formation (central tropical Atlantic near 17.5N-44W)

IOH 72 Hr Outlook (0000Z Aug 30)… 60% chance of tropical cyclone formation (central Atlantic near 21N-41W)

IOH 96 Hr Outlook (0000Z Aug 31)… 30% chance of tropical cyclone formation (eastern Atlantic near 25N-39.8W)

IOH 120 Hr Outlook (0000Z Sep 1)… 30% chance of tropical cyclone formation (eastern Atlantic near 30N-39W)

AREA OF INTEREST #3…Satellite imagery over central Africa… estimated location of the tropical wave of interest is shown by the yellow circle:

Based on the latest satellite imagery… a tropical wave of low pressure is over central Africa in the vicinity of 8N-9E. Computer models have been gung-ho on developing this wave as it moves into the eastern tropical Atlantic after day 4… therefore I have introduced this wave as an area of interest for development in the coming days. Odds of development at day 5 are currently set to a low 10% as it is generally rare for a wave to immediately develop into a tropical cyclone just offshore of Africa. Development odds will likely be notably higher than this once the wave continues further offshore… especially if the models continue to forecast the robust development to be aided by the low shear and upper outflow of the east tropical Atlantic upper ridge.

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

IOH 24 Hr Outlook (0000Z Aug 28)… 0% chance of tropical cyclone formation (central Africa near 8N-4E)

IOH 48 Hr Outlook (0000Z Aug 29)…0% chance of tropical cyclone formation (western Africa near 8.5N-1W)

IOH 72 Hr Outlook (0000Z Aug 30)…0% chance of tropical cyclone formation (western Africa near 9N-6W)

IOH 96 Hr Outlook (0000Z Aug 31)… 0% chance of tropical cyclone formation (western Africa near 9.5N-12W)

IOH 120 Hr Outlook (0000Z Sep 1)… 10% chance of tropical cyclone formation (offshore of western Africa near 10N-17.5W)


...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 Tropical Storm Ida… was initialized as a tropical depression as model run was before tropical storm strength reached… crosses the western Cayman Islands as a tropical depression at 18 hours… crosses western Cuba as a tropical storm at 30 hours… makes landfall as an intense hurricane over southeast Louisiana at 72 hours… weakening inland remnant low located over western Tennessee at 120 hours

**For area of interest #1... no tropical cyclone formation shown (transitions to elongated non-tropical frontal low near 35N-45W at 84 hours).

**For area of interest #2... tropical cyclone formation suggested near 14N-46W at 30 hours… after turning north weakens to a remnant low near 20N-48W at 84 hours

**For area of interest #3…tropical wave forecast to emerge from Africa at 90 hours... tropical cyclone formation suggested due south of the Republic of Cabo Verde Islands at 126+ hours

**South fragment of tropical wave associated with area of interest #2 forecast to strengthen into a central Caribbean tropical low near 15N-81W at 138 hours


1200Z ECMWF Model Run…

**For Tropical Storm Ida… was initialized as a tropical depression as model run was before tropical storm strength reached… passes through the western Cayman Islands and western Cuba as a tropical storm thru 36 hours… makes landfall over south-Central Louisiana as a hurricane at 96 hours… as an inland weakening tropical storm the center reaches southeast Arkansas at 120 hours.

**For area of interest #1...Tropical cyclone formation suggested near 32N-50W at 48 hours… reaches top-end tropical storm status by 72 hours while reaching 35N-46W… by 120 hours while rapidly accelerating northeast over cooler water transitions into a non-tropical frontal cyclone near 46N-32.5W.

**For area of interest #2... tropical cyclone formation suggested near 13.5N-46W at 24 hours… after turning north weakens to a remnant low near 23.5N-51.5W at 120 hours

**For area of interest #3… tropical wave forecast to emerge from Africa at 96 hours... rapidly intensifying tropical cyclone suggested offshore of Africa near 10.5N-19.5W at 120 hours.


1800Z GFS Model Run...

**For Tropical Storm Ida... passes over the Cayman Islands with a compact and briskly strengthening core at 9 hours… compact core crosses western Cuba at hurricane strength at 24 hours… makes landfall as an intense hurricane over southeast Louisiana at 69 hours… inland remnant low centered over the Mississippi/Alabama/Tennessee border at 120 hours.

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

**For area of interest #2... tropical cyclone formation suggested near 13N-44W at 12 hours… after turning north and reaching high-end tropical storm status it weakens into a remnant low at 87 hours located near 20.5N-43W

**For area of interest #3… tropical wave forecast to emerge from Africa at 108 hours... development in long range (after 168 hours) suggested west-southwest of the Republic of Cabo Verde Islands

**South fragment of tropical wave associated with area of interest #2 forecast to strengthen into a central Caribbean tropical low near 14N-80W at 138 hours

1200Z NAVGEM Model Run...

**For tropical storm Ida... was initialized as a tropical depression as model run was before tropical storm strength reached… crosses the western Cayman Islands as a tropical storm at 18 hours… crosses western Cuba as a tropical storm at 36 hours… makes landfall over south-Central Louisiana as an intense hurricane at 84 hours… as an inland weakening tropical storm the center reaches southeast Arkansas at 120 hours.

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

**For area of interest #2... tropical cyclone formation shown near 13.5N-45W at 24 hours… turns northeast in track and reaches 27.5N-39.8W at 120 hours at hurricane strength.

**For area of interest #3…tropical wave forecast to emerge from Africa at 120 hours... tropical cyclone formation suggested over the southern Republic of Cabo Verde Islands at 150 hours

**Tropical wave currently over Western Africa emerges into the Atlantic at 48 hours… develops low pressure spin near 12N-31.5W… does not develop further due to dominance of area of interest #3 to the east.

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