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 #95 (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.**********


...MONDAY AUGUST 30 2021 5:59 AM EDT...

Satellite image as of 2340Z. 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 and depression Ten sections below for an update on all active Atlantic tropical systems. See Julian section below for final remarks on what was a short-lived tropical storm in the open central Atlantic. See area of interest sections below for all areas being monitored for tropical cyclone formation in the Atlantic (note area of Interest #3 was only recently added to the NHC outlook product & after the above charts were made… which Is why it is labeled as not being in the NHC outlook in the above charts when it now is.

Elsewhere… another tropical wave of low pressure… located east of area of interest #1 over central Africa… is also showing less organized thunderstorms that are also not as widespread in coverage. Therefore I have not added this wave as an area of interest at this time.


MAJOR HURRICANE IDA (RECENTLY DOWNGRADED TO TROPICAL STORM IDA)… Initially after landfall in southeast Louisiana… powerful Hurricane Ida was slower to weaken due to the healthy low shear and upper outflow environment and perhaps the moisture content of the southeast Louisiana marshland. However as Ida’s center has moved further inland and into southern Mississippi early this morning… the weakening rate has finally quickened… dropping to category 2 105 mph max sustained winds as of 0000Z earlier tonight… and the hurricane is now a minimal category 1 with 75 mph max sustained winds as of this writing (update as of 5 AM EDT… Ida has weakened to a tropical storm with 60 mph max sustained winds). The inland track is expected to bend more northeast and east with time while Ida chases the surface ridge weakness being induced by the current central Canada frontal low. After 24 hours… Ida is expected to transition 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. Over the last couple of days the models have trended with a more amplified shortwave upper trough in response to a more amplified upper trough/surface frontal system moving into western North America whose warm sector more strongly amplifies upper ridging over the US (this stark shift in the modeling is visible by comparing the 12Z runs of the ECMWF from Friday August 27 and Sunday August 29… the earlier run having no/weak frontal low over Canada by 12Z September 4 whereas a stronger frontal low is present on the later run over Canada). The resulting more amplified shortwave upper trough is shown to cause Ida’s remnants… or alternatively the south side of its remnants… to evolve into a subtropical or tropical system offshore of the southeast US in 4 to 5 days supported by the lower shear and increased eastern divergence zone of the south base of the more amplified upper trough. If these model trends continue… we could very well be making Ida’s remnants an area of interest for tropical development offshore of the southeast US.


Here are observations of peak wind (in mph) generated by Ida and logged by National Weather Service stations over the last several hours:

**Grand Isle LA… sustained 64… gust 95 (record before instrument failed at 3:55 PM CDT)

**New Orleans LA… sustained 49… gust 84 (record before instrument failed at 5:53 PM CDT)

**Hammond LA… sustained 35… gust 56 (7:44 PM CDT… note instrument has recently failed)

**Baton Rouge LA… sustained 26… gust 52 (10:53 PM CDT)

**Gulfport MS… sustained 33… gust 63 (7:53 PM CDT)

**McComb MS… sustained 23… gust 43 (now)

**Hattiesburg MS… sustained 18… gust 31 (10:53 PM CDT)

**Jackson MS… sustained 15… gust 29 (now)

**Mobile AL… sustained 22… gust 39 (now)

**Monroeville AL… sustained 12… gust 22 (now)


**Tropical storm force winds with some damage potential have spread well inland across southeast Louisiana... southern Mississippi... and southwestern Alabama. Avoid unnecessary treacherous travel in the heavy rains and gusty winds if possible through this morning.

**Heavy rains with flash flooding potential from Ida and its remnants will spread across Mississippi and Alabama today… then Tennessee… Kentucky… West Virginia… and possibly into the mid-Atlantic and northeastern US over the next couple of days or so.

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

0 Hr Position (0000Z Aug 30)… 105 mph maximum sustained wind hurricane centered over southeast Louisiana at 30.3N-90.7W

IOH 24 Hr Forecast (0000Z Aug 31)… 35 mph maximum sustained wind tropical depression centered over northeastern Mississippi at 34N-89W

IOH 48 Hr Forecast (0000Z Sep 1)… remnant low centered over Kentucky at 37.5N-85.5W

TROPICAL DEPRESSION TEN... Depression Ten still 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 upper vorticity to the north. However the depression is in a spot of lower shear in between the upper vortex to the northeast and vorticity string to the northwest as previously Forecast… and with thunderstorm bursts that covered the center made a pass at trying to become a tropical storm around 1200Z yesterday and is trying again per the latest satellite frames. By 24 and thru 48 hours… the upper vorticity string to the northwest will near this system and increase the shear again… so my intensity projection thru that time is still a depression. The GFS still shows the upper vorticity string staying more consolidated instead of being strung out over this system and killing it off while suppressing upper divergence… which still gives a chance for this system to survive while sneaking under the east edge of the vorticity string… and so the general idea is that the depression survives in the short term. And if it does survive… it could be rewarded while moving into lower shear and upper outflow environment beneath mid-latitude upper ridging at days 3 to 5 as the NAVGEM and GFS currently suggest. For now… I forecast only slow strengthening to 50 mph max sustained winds in that timeframe (lower than the NHC Forecast) as we still don’t know for sure if this system will survive in the shorter term… which could result in larger error if forecasting bullish strengthening. However the intensity forecast would in fact need an upward adjustment if indeed we find the depression surviving and taking advantage of the better upper winds in the longer range.


Forecast track is adjusted west as the depression did not become a tropical storm tall enough to be dragged on an east angle by the upper westerly flow. The track bends west thru 96 hours while the east cell of the Atlantic surface ridge intensifies while aided by the western convergence zone of the upper trough interacting with Julian. By 120 hours the track bends north again in the flow between the Atlantic surface ridge and approaching remnants of Ida to the west.

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

0 Hr Position (0000Z Aug 30)… 35 mph maximum sustained wind tropical storm centered at 20.1N-50.6W

IOH 24 Hr Forecast (0000Z Aug 31)… 35 mph maximum sustained wind tropical depression centered at 22.8N-50.6W

IOH 48 Hr Forecast (0000Z Sep 1)… 35 mph maximum sustained wind tropical depression centered at 26N-51W

IOH 72 Hr Forecast (0000Z Sep 2)… 45 mph maximum sustained wind tropical storm centered at 28.5N-54W

IOH 96 Hr Forecast (0000Z Sep 3)… 50 mph maximum sustained wind tropical storm centered east of Bermuda at 32N-59.5W

IOH 120 Hr Forecast (0000Z Sep 4)… 50 mph maximum sustained wind tropical storm centered at 36N-57.5W


TROPICAL STORM JULIAN (RECENTLY DOWNGRADED TO A FRONTAL CYCLONE)…Julian has been a short-lived tropical storm while the cold front of the northwest Atlantic frontal low has overspread the circulation… with the dry cooler air behind the front causing Julian to lose thunderstorm activity over the center even before having the chance to reach cooler water. Julian is now a gale-force remnant cyclone along the front being aided by non-tropical means… while supported by the eastern divergence zone of the upper trough associated with the northwest Atlantic frontal low. The remnant cyclone of Julian and frontal low are forecast to merge and contribute to rough seas south of Greenland… this is my final statement on Julian on this blog as it is no longer a tropical system.


AREA OF INTEREST #1… The vigorous tropical wave of low pressure over western Africa has arrived to the west coast with rotation and large masses of thunderstorms. Computer models have remained gung-ho on developing this wave as it moves into the eastern tropical Atlantic… therefore I have begun a tropical cyclone formation Forecast as outlined below… but wait till 48 hours before forecasting genesis as the wave does not yet have a well-defined center of spin with banding features. This wave will be aided by the low shear and upper outflow of the east tropical Atlantic upper ridge… and I forecast a ramp up to category 2 hurricane by day 5 as all the global models remain very bullish on developing this system. The first surface ridge weakness this system will deal with is to be generated in the far east Atlantic by the divergence zone of a northeast Atlantic upper vortex to be deposited by the upper trough currently interacting with Julian. Curiously the GFS has consistently shown an early northward turn into this weakness while entangling this system with an adjacent tropical wave to the east… resulting in a merger with the adjacent wave that slows the west progress of this system and allows it to fall north into the weakness. The other models have this system moving due west over the next five days while escaping the developing weakness off to the northeast… and this is also the forecast I am going with as I see no reason that this wave will merge with the adjacent wave as the two have good spacing between each other on Meteosat satellite imagery (https://www.goes.noaa.gov/f_meteo.html)

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

0 Hr Position (0000Z Aug 30)… Tropical low pressure located on west coast of Africa at 10N-14W

IOH 24 Hr Forecast (0000Z Aug 31)… Tropical low pressure located offshore of western Africa at 10.5N-19W

IOH 48 Hr Forecast (0000Z Sep 1)… 45 mph maximum sustained wind tropical storm centered due south of the Republic of Cabo Verde Islands at 11N-24W

IOH 72 Hr Forecast (0000Z Sep 2)… 65 mph maximum sustained wind tropical storm centered at 11.5N-29W

IOH 96 Hr Forecast (0000Z Sep 3)… 85 mph maximum sustained wind hurricane centered at 12N-34W

IOH 120 Hr Forecast (0000Z Sep 4)… 100 mph maximum sustained wind hurricane centered at 12.5N-39W


AREA OF INTEREST #2… An area of low surface pressure offshore of the US east coast and Delmarva peninsula has been left behind by the tail end of the cold front associated with the current northwest Atlantic frontal low… and has been introduce into the NHC Outlook products over the last day. The low pressure area has struggled to produce thunderstorms despite being under a vast area of upper ridging which promotes upper outflow. Perhaps this is an effect of dry air to the northeast caused by the sinking motion underneath the western convergence zone of the northwest Atlantic upper trough. While the NHC now forecasts 0% development odds due to the potential for shear from the approach of the current Central Canada upper trough… the eastern divergence zone of the upper trough may give this low pressure area what it needs to finally fire thunderstorms. Plus the GFS shows the incoming upper trough not digging south into the upper ridging… so wind shear may not increase substantially. Therefore I hang on to this system as an area of interest until the Forecast track brings it to cooler water at day 4. However I have low development odds as none of the global models ever showed this system developing. This system has been trapped stationary within the west cell of the Atlantic surface ridge… but the north side of the cell will erode courtesy of the approaching Central Canada frontal low… with the south edge of the frontal low pushing this system on a gradual east-northeast acceleration out to sea

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

IOH 24 Hr Outlook (0000Z Aug 31)… 10% chance of tropical cyclone formation (offshore of the northeast US near 37N-72.5W)

IOH 48 Hr Outlook (0000Z Sep 1)… 10% chance of tropical cyclone formation (northwest Atlantic near 39N-67W)

IOH 72 Hr Outlook (0000Z Sep 2)… 10% chance of tropical cyclone formation (northwest Atlantic near 40.5N-59W)

IOH 96 Hr Outlook (0000Z Sep 2)… 0% chance of tropical cyclone formation (north Atlantic near 42.5N-50W)


AREA OF INTEREST #3…The tropical wave of

low pressure that spawned tropical depression ten is currently inactive while entering the eastern Caribbean Sea from the Lesser Antilles. 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 avoids shearing the wave as it weakens from being cut-off from high-latitude cold air… a pattern similar to the genesis of Ida when its seedling wave was in the Caribbean. In fact poleward outflow into this upper vorticity has started to enhance thunderstorms downstream of the wave and over northwest Colombia and offshore southern Caribbean water… and this wave could merge with that activity in the 3 to 5 day window. Therefore I have added this wave as an area of interest for tropical development… and the NHC has also done so recently in their outlook product. The CMC model has been the only global model showing development… and so development odds are kept low. However I am a notch above the NHC product by day 5 due to the favorable upper wind outlook. By days 3 to 5 I forecast this system to stay north of the Central America land mass due to the ridge weakness to be created by Ida’s remnants… but a sharp north turn is not anticipated either due to the eastern US surface ridge forecast to be west of Ida’s remnants and induced by the western convergence zone of the amplified upper trough forecast to support Ida’s remnants.

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

IOH 24 Hr Outlook (0000Z Aug 31)…0% chance of tropical cyclone formation (eastern Caribbean Sea near 13N-65W)

IOH 48 Hr Outlook (0000Z Sep 1)…0% chance of tropical cyclone formation (central Caribbean Sea near 13N-70W)

IOH 72 Hr Outlook (0000Z Sep 2)…0% chance of tropical cyclone formation (central Caribbean Sea near 13.5N-75W)

IOH 96 Hr Outlook (0000Z Sep 3)…20% chance of tropical cyclone formation (central Caribbean Sea near 14.5N-80W)

IOH 120 Hr Outlook (0000Z Sep 4)…30% chance of tropical cyclone formation (western Caribbean Sea near 16N-84W)

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