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 #94 (Weekend Edition)

*******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 11:08 PM EDT...

Satellite image as of 0110Z. 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 1200Z:

GFS Model Upper-Level Winds 1200Z:

See Ida section below for the latest on the hurricane expected to impact parts of the US Gulf coast tomorrow. See tropical depression ten section below for an update on the new depression located out in the middle of the central tropical Atlantic. See area of interest #1 and #2 sections for updates on other areas being monitored for tropical development in the Atlantic.


Elsewhere… another tropical wave of low pressure… located east of area of interest #2 over central Africa… is also showing organized and concentrated thunderstorms. This tropical wave may also become another area of interest for development in the eastern tropical Atlantic in the coming days. In addition… the tropical wave that spawned tropical depression ten is now inactive while en route to the Caribbean. The current cool core upper vorticity string in the west Atlantic is forecast to potentially enhance the poleward outflow of the tropical wave as it moves across the Caribbean as the upper vorticity only lightly shears the wave as it collapses from being cut-off from high-latitude cold air… a pattern similar to the genesis of Ida when it was in the Caribbean. Therefore this tropical wave may also become another area of interest for tropical development as it moves across the Caribbean over the next few days.


HURRICANE IDA... While moving northwest across the Gulf of Mexico… Ida has not intensified as much as previously thought despite an expansive low shear and upper outflow environment… healthy core structure with defined eye… and warm 29 to 30 deg C waters. The answer could be related to the lingering upper vorticity in the western Gulf whose central and western upper convergence zones have created a dry sinking air pocket… and perhaps this dry air has been disrupting the thunderstorm bands around the eye of Ida as seen by the occasional ragged appearance of the bands on colorized infrared satellite throughout the day. However make no mistake… Ida is still a potent category 2 hurricane still capable of damage. The track is expected to bend more north and take the hurricane into southeastern Louisiana in the next 24 hours… and then after landfall leans east while Ida chases the surface ridge weakness to be induced by the current developing north-central US frontal low as that frontal low and it’s upper trough sweep across southeastern Canada. After 48 hours while inland over the southeast US… 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…. with the remnant low currently forecast by models to reach the coastal northeast US region in about 5 days.


Regarding the intensity forecast… tonight I have gone a notch lower than the NHC as of this writing and bring Ida into southeast Louisiana as a still dangerous category 3… but even if Ida does not strengthen further it is still a potent category 2.


With these forecast updates… the following impacts are expected:

**Interests across the United States Gulf coast in the hurricane and tropical storm advisory region across Louisiana... Mississippi... and Alabama should be finishing preparations a the hurricane will arrive tomorrow. Preparations should have included 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 in southeast Louisiana near the center of where Ida comes in is expected to be significant… even if Ida comes in as a category 2.

**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 tomorrow and into Monday... finish 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.

**Heavy rains with flash flooding potential from Ida and its remnants will spread onshore late Sunday and into early next week across southeast Louisiana… Mississippi… western Florida panhandle… Alabama… and possibly into the mid-Atlantic and northeastern US later on.

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

0 Hr Position (1800Z Aug 28)… 105 mph maximum sustained wind hurricane centered in the Gulf of Mexico at 26.2N-87W

IOH 24 Hr Forecast (1800Z Aug 29)… 125 mph maximum sustained wind major hurricane making landfall on the southeast Louisiana coast at 29.5N-89.8W

IOH 48 Hr Forecast (1800Z Aug 30)… Remnant low centered over northeastern Mississippi at 33.6N-89W


TROPICAL DEPRESSION TEN... The low pressure spin seeded by the tropical wave in the central Atlantic has become tropical depression ten in the last 24 hours. The depression has the classic look of a sheared tropical cyclone with the strongest thunderstorms pulled off to the east of the surface swirl center… with the shear imparted by an upper vortex that has arrived to the north. The depression has at long last turned north into the surface ridge weakness induced by area of interest #1… but took longer to do so and is therefore a bit South and west of the prior forecast. My updated one is adjusted accordingly.


I still forecast some strengthening to a tropical storm by 24 hours when the shear potentially reduces as the 12Z GFS model run still suggested the cool core upper vortex weakening while cut-off from high-latitude cold air… and also showed the vortex shifting a bit northeast and away. The weakening after 24 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. Comparing the 12Z GFS from today with yesterday’s 18Z GFS…. the deposited upper vorticity is more consolidated into an upper vortex instead of being strung out over this system and killing it off while suppressing upper divergence. This gives a chance for this system to survive while passing under the edge of the Forecast upper vortex… and I no longer Forecast this system to quickly dissipate. If it does survive… it could be rewarded while moving into lower shear and upper outflow environment beneath mid-latitude upper ridging at days 4 and 5 as the CMC and NAVGEM suggested. For now… I forecast only slow strengthening in that timeframe as we still don’t know if this system will survive in the shorter term. The forecast track has an east lean at 48 hours as I predict a strong/tall enough structure at 24 hours that will allow the system to be leaned by the upper winds associated with the second round of upper vorticity. The track bends more north and then northwest by 72+ hours as the eastern Atlantic surface ridge cell will strengthen and expand 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 (1800Z Aug 28)… 35 mph maximum sustained wind tropical depression centered at 15.6N-50W

IOH 24 Hr Forecast (1800Z Aug 29)… 45 mph maximum sustained wind tropical storm centered at 18.5N-50W

IOH 48 Hr Forecast (1800Z Aug 30)… 35 mph maximum sustained wind tropical depression centered at 22.5N-48.5W

IOH 72 Hr Forecast (1800Z Aug 31)… 35 mph maximum sustained wind tropical depression centered at 26N-48.5W

IOH 96 Hr Forecast (1800Z Sep 1)… 45 mph maximum sustained wind tropical storm centered at 28.5N-51W

IOH 120 Hr Forecast (1800Z Sep 2)… 50 mph maximum sustained wind tropical storm centered at 33N-55W


AREA OF INTEREST #1 (RECENTLY UPGRADED TO TROPICAL DEPRESSION ELEVEN)… The surface low pressure area in the open central Atlantic… located near 33N-50W… has not gotten better organized thunderstorm-wise… but the surface spin has gotten better defined with time such that only a small increase in thunderstorm intensity and organization would allow this system to become a tropical depression. This system is turning east in the flow out ahead of the northwest Atlantic upper trough and it’s surface frontal low. The upper trough is forecast to amplify while sliding across the North Atlantic… and is coming in a little more amplified than previously Forecast when comparing the 12Z GFS from today to yesterday’s 18Z GFS. This will reduce the shear and increase the upper divergence over this system… and given the system is on the cusp of tropical cyclone status I have sharply raised odds of development to 90% (the NHC has done likewise with 80% odds as of this writing). The forecast track is adjusted more west due to the current position of this system… and also more north to reflect the more southerly steering flow as the upper trough is coming in a bit more amplified. By 48 hours… this system will reach cooler waters and this is when I drop odds of tropical development to 0%. The upper divergence supplied by the upper trough could allow this system to ramp up quickly to a mid-strength tropical storm in the next 24 hours… followed by transition into a gale force frontal cyclone once it reaches cooler waters at 48 hours… with gale force strength likely at that time and beyond even if this system does not become a tropical cyclone to begin with.


Update as of 11 PM EDT… this surface low pressure area has recently developed more organized thunderstorms and is now tropical depression eleven. I will have a special update on this system later tonight or tomorrow morning.

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

IOH 24 Hr Outlook (1800Z Aug 29)… 90% chance of tropical cyclone formation (central Atlantic near 36N-44W)

IOH 48 Hr Outlook (0000Z Aug 31)… 0% chance of tropical cyclone formation (northeast Atlantic near 41N-39W)

AREA OF INTEREST #2… Based on the latest satellite imagery… a tropical wave of low pressure is over western Africa in the vicinity of 9N-9W with an increasing thunderstorm mass on its west side. Computer models have remained gung-ho on developing this wave as it moves into the eastern tropical Atlantic… therefore I forecast a very high 90% chance of tropical cyclone formation by days 4 and 5 (the NHC outlook is at 70% by day 5 as of this writing). 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… my next update will have a tropical cyclone formation forecast with specific track and intensity points.

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

IOH 24 Hr Outlook (1800Z Aug 29)… 0% chance of tropical cyclone formation (west coast of Africa near 10N-14W)

IOH 48 Hr Outlook (1800Z Aug 30)… 20% chance of tropical cyclone formation (offshore of western Africa near 10.5N-19W)

IOH 72 Hr Outlook (1800Z Aug 31)… 60% chance of tropical cyclone formation (eastern tropical Atlantic due south of the Republic of Cabo Verde Islands near 11N-24W)

IOH 96 Hr Outlook (1800Z Sep 1)… 90% chance of tropical cyclone formation (eastern tropical Atlantic near 11.5N-29W)

IOH 120 Hr Outlook (1800Z Sep 1)…90% chance of tropical cyclone formation (eastern tropical Atlantic near 12N-34W)

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