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 

 
 
Search
  • NCHurricane2009

MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #93 (Weekend Edition)

Updated: Aug 29

*******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 28 2021 1:49 AM EDT...

Satellite image as of 0440Z. 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 Ida section below for the latest on the hurricane expected to significantly intensify en route to the US Gulf coast this weekend. See area of interest #1 through #3 sections for updates on all other areas being monitored for tropical development in the Atlantic.


HURRICANE IDA... Ida has put on an impressive intensification burst while approaching and then crossing western Cuba… becoming a category 1 hurricane after only being a minimal tropical storm only 24 hours ago. Ida’s center is now in the southeast edge of the Gulf of Mexico… and will continue on a northwest heading while rounding the southwest side of the Atlantic surface ridge. The track forecast bends more north and then leans east at days 2 to 4 due to the surface ridge weakness of a forecast frontal low passing through southeastern Canada. By day 4 while inland over the southeast US in the vicinity of the Appalachian Mountains… Ida is expected to continue northeast as it transitions into a remnant non-tropical frontal low supported by the eastern divergence zone of a shortwave upper trough to stream across the US/Canada border region.


Regarding the intensity forecast… there is not good news for the southeast Louisiana and Mississippi US Gulf coast region as Ida has emerged from northwest Cuba with a healthy structure on infrared satellite featuring a tight core with spiral banding features around an eye-type feature. Keep in mind Ida has strengthened briskly thus far while being interrupted by light westerly shear from the upper vorticity just to the west… so imagine its potential once that upper vorticity dissipates in the next 12 to 24 hours and leaves Ida underneath expansive upper ridging with low shear and upper outflow. Plus the water temps in the Gulf are running at a high 29 to 30 deg C. Given the improved Storm structure and very favorable conditions that lie ahead… I have opted to raise the intensity forecast a notch above the previous one I had in special update #92A and also the NHC… and I now predict a stronger category 4 with 145 mph maximum sustained winds for the landfall in the southeast Louisiana or Mississippi coast. I have not forecasted an intensity higher than this at present as the thunderstorm intensity on colorized infrared satellite has not been intense since Ida emerged from Cuba.


With these forecast updates… the following impacts are expected:

**Interests on the northwestern Cuban coast will see coastal sea swells until Ida pulls further away.

**Interests in the Florida Keys could see coastal sea swells and are seeing heavy rain that will last through tonight from the outer northeast bands of Ida.

**Interests across the United States Gulf coast in the hurricane and tropical storm advisory region across Louisiana... Mississippi... and Alabama should continue preparing for what is forecast to be a strong and potentially historic 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. Wind damage near the center of where Ida comes in is expected to be catastrophic… but pinpointing the exact landfall location of the center is hard to do this early. However the chances for the center’s landfall in Alabama or southwest Louisiana appear low… with the chance much higher in south-Central and southeast Louisiana as well as Mississippi. 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... continue 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 28)… 80 mph maximum sustained wind hurricane centered just offshore of northwest Cuba at 23N-84W

IOH 24 Hr Forecast (0000Z Aug 29)… 125 mph maximum sustained wind major hurricane centered in the Gulf of Mexico at 26.5N-87.5W

IOH 42 Hr Forecast (1800Z Aug 29)… 145 mph maximum sustained wind major hurricane making landfall on the southeast Louisiana coast at 29.5N-89.8W

IOH 48 Hr Forecast (0000Z Aug 30)... 135 mph maximum sustained wind major hurricane centered over southeastern Louisiana at 30N-90W

IOH 72 Hr Forecast (0000Z Aug 31)... 35 mph maximum sustained wind tropical depression centered over northeastern Mississippi at 33.8N-88.9W

IOH 96 Hr Forecast (0000Z Sep 1)… remnant low centered over Kentucky at 37.5N-85.5W


AREA OF INTEREST #1... The surface low pressure area in the open central Atlantic has not gotten better organized despite an improved structure and low shear beneath the Central Atlantic upper ridge… as the low pressure has struggled to maintain vigorous thunderstorms. This system is expected to turn to the east while falling into the surface ridge weakness associated with the current North Atlantic front. The ridge weakness will be maintained by the arrival of the current eastern 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 72 hours.


Wind shear is expected to increase soon as the nearby upper vorticity in the northwest Atlantic nears… with the shear through 48 hours as the current upper trough from eastern Canada is still forecast to take a longer time to become amplified. Therefore my development odds are low as the shear forecast has remained negative. Despite a more amplified upper trough with lower shear and a healthy eastern divergence zone by 72 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 29)… 35% chance of tropical cyclone formation (central Atlantic near 33N-47.5W)

IOH 48 Hr Outlook (0000Z Aug 30)… 35% chance of tropical cyclone formation (central Atlantic near 35N-42.5W)

IOH 72 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 in the central Atlantic has lost some organization as shear begins to increase with the approach of upper vorticity to the north. However a recent strong burst of thunderstorms makes this system resemble a sheared tropical cyclone… and so I have begun a tropical cyclone formation Forecast as outlined below.


Satellite animation reveals this system is still drifting west… and so my Forecast position at 24 hours is a tad west of the current position while this system makes a long awaited north turn into the surface ridge weakness to be induced by area of interest #1. The forecast track is shifted west of previous as this system has taken a long time to slow down its west travel and is now unlikely to reform northeast into the eastern divergence zone of the upper vorticity. I currently forecast a weak tropical storm with peak strength at 48 hours when the shear potentially reduces as the 18Z GFS model run suggested by showing the cool core upper vorticity collapse…perhaps from the latent heat release of this system’s thunderstorms. The weakening after 48 hours is forecast from another round of shear from upper vorticity to be deposited by the upper trough to interact with area of interest #1… and I forecast dissipation by 96 hours as the forecast track moves this system directly below the upper vorticity where there is a lack of upper divergence. The forecast track has an east lean at 72 hours as I predict the peak strength at 48 hours will allow the system to have a tall enough structure to be leaned by the upper winds associated with the second round of upper vorticity. The track bends more north by 96 hours as the shear should weaken this system to a shallow vortex steered by the west end of the eastern Atlantic surface ridge cell which will expand further when aided by the western convergence zone of the upper trough to interact with area of interest #1.

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

0 Hr Position (0000Z Aug 28)… Tropical low pressure centered at 13.8N-49W

IOH 24 Hr Forecast (0000Z Aug 29)… 40 mph maximum sustained wind tropical storm centered at 17.5N-49.5W

IOH 48 Hr Forecast (0000Z Aug 30)… 45 mph maximum sustained wind tropical storm centered at 20.5N-49.5W

IOH 72 Hr Forecast (0000Z Aug 31)… 35 mph maximum sustained wind tropical depression centered at 25N-47.5W

IOH 96 Hr Outlook (0000Z Sep 1)… Remnant low centered at 27.5N-47.5W


AREA OF INTEREST #3… Based on the latest satellite imagery… a tropical wave of low pressure is over central Africa in the vicinity of 9N-2E. Computer models have been gung-ho on developing this wave as it moves into the eastern tropical Atlantic after day 3… therefore the NHC has recently added this wave as an area of interest for development in their Outlook products. I agree with the NHC’s already raised 30% odds of development by day 5… and will support showing even higher odds in future updates 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 29)…0% chance of tropical cyclone formation (western Africa near 9N-3W)

IOH 48 Hr Outlook (0000Z Aug 30)…0% chance of tropical cyclone formation (western Africa near 9.5N-8W)

IOH 72 Hr Outlook (0000Z Aug 31)… 0% chance of tropical cyclone formation (western Africa near 10N-13W)

IOH 96 Hr Outlook (0000Z Sep 1)… 20% chance of tropical cyclone formation (offshore of western Africa near 10.5N-19W)

IOH 120 Hr Outlook (0000Z Sep 2)… 30% chance of tropical cyclone formation (eastern tropical Atlantic due south of the Republic of Cabo Verde Islands near 11N-24W)

31 views0 comments