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 #96

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


...TUESDAY AUGUST 31 2021 1:18 AM EDT...


See Ida section below for more info on the rainfall flood risk the remains of the former hurricane poses to a large swath of the eastern United States. See Tropical Storm Kate section below for an update on the only currently active Atlantic tropical cyclone. See area of interest sections below for all areas being monitored for tropical cyclone formation in the Atlantic


Elsewhere… another tropical wave of low pressure… located east of area of interest #1 over western Africa… is producing vigorous thunderstorm activity. The wave is likely to turn northwest toward a surface ridge weakness to develop in the far east Atlantic while also pushed by the developing wave associated with area of interest #1. This will tend to move the wave into cooler waters and also toward dry Saharan air after it moves offshore into the Atlantic in the coming days… therefore I have not added this wave as an area of interest for tropical development at this time.


TROPICAL STORM IDA (RECENTLY DOWNGRADED TO REMNANTS OF IDA)… After slamming southeast Louisiana with hurricane conditions and widespread damage… and after bringing tropical storm conditions to southern Mississippi and southwestern Alabama… Ida as of 5 PM EDT weakened further to a tropical depression centered over Mississippi. The final NHC advisory on Ida expired at 11 PM EDT with the weather prediction center (WPC) now taking over advisories due to the ongoing rainfall flood threat… which basically makes Ida an inland remnant tropical low pressure. My updated forecast track is nudged south and west due to the current position of Ida relative to the previous forecast.


The track of Ida’s remnants is expected to bend more northeast and east with time while chasing the surface ridge weakness being induced by the current eastern Canada frontal low. In the next 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. Models continue to trend 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 strongly amplifies upper ridging over the US. Today’s model runs resolve this scenario a little differently… instead of the more amplified shortwave upper trough transitioning Ida’s remnants into a subtropical system offshore of the eastern or southeastern US… today’s runs show Ida’s remnant frontal low intensify into a frontal cyclone over the coastal northeast US on Thursday due to the increased divergence on the east side of the more amplified upper trough… with the remnant cyclone continuing to intensify in the vicinity of Nova Scotia and Newfoundland by Friday or Saturday. Ida’s remnants will still drive a cold front into the waters offshore of the southeast US late this week or by Saturday… and will see if models forecast a subtropical or tropical system boosted by the upper divergence on the southeast end of the amplified upper trough… so far the CMC has hinted at this.


**Based on the latest forecast track and latest Doppler radar… in the coming days Ida’s remnants will spread heavy rains with flash flooding potential will spread across northeast Mississippi… Alabama… northwest Georgia…. Tennessee… the western Carolinas… Kentucky… southern Ohio… West Virginia… Virginia… Pennsylvania… Maryland… Delaware… New Jersey… southeastern New York state… Connecticut… Rhode Island… Massachusetts… southern Vermont… southern New Hampshire… and southern Maine. As of this writing… an impressive swath of flash flood watches covers much of this region as of this writing. If you encounter a flooded roadway… do not drive into it to avoid drowning! Mudslides may occur in the Appalachian mountain region.

**There is potential for the remnant low to strengthen into a frontal cyclone that brings gusty winds to the coastal northeastern United States on Thursday… with stronger potentially damaging winds arriving to Nova Scotia or Newfoundland by Friday or Saturday as the remnant cyclone strengthens further.


This is my final statement on Ida on this blog as it is no longer a tropical cyclone. Additional remarks on Ida’s remnants will be on the home page bulletins of this site for the duration of time Ida’s remnants bring impacts land areas.

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

0 Hr Position (0000Z Aug 31)… 35 mph maximum sustained wind tropical depression centered over central Mississippi at 32.8N-89.7W

IOH 48 Hr Forecast (0000Z Sep 1)… remnant low centered over southern Tennessee at 37.5N-86W


TROPICAL STORM KATE... Feisty tropical depression ten has been able to fire enough thunderstorm bursts close to the center in the midst of westerly shear to finally become Tropical Storm Kate within the last 24 hours… even reaching an estimated peak of 45 mph maximum sustained winds. The thunderstorm bursts have been too intermittent to keep Kate at that strength… with the estimated strength falling to 40 mph max sustained winds as of late. The current northwest Atlantic upper trough will push a string of upper vorticity toward Kate in the next 24 hours. The GFS still shows the upper vorticity string staying more consolidated instead of being strung out over Kate and killing it off while suppressing upper divergence… which still gives a chance for Kate to survive the next 24 hours while sneaking under the east edge of the vorticity string… and so my forecast for now assumes Kate survives. And if it does survive… Kate could be rewarded while moving into lower shear and upper outflow environment beneath mid-latitude upper ridging at 2+ days. For now… I forecast only slow strengthening to 50 mph max sustained winds in that timeframe as we still don’t know for sure if Kate 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 Kate surviving and taking advantage of the better upper winds in the longer range. Interestingly all of the global models as of late have abandoned the idea of Kate surviving… and the NHC has swung their intensity forecast downward and is now below instead of above my intensity projection.


Forecast track in the short-term is adjusted w touch west due to Kate’s current position. The track bends west thru 72 hours while the east cell of the Atlantic surface ridge intensifies while aided by the western convergence zone of the upper trough in the northwest Atlantic as that trough slides into the northeast Atlantic. By 96+ hours the track bends northeast in the flow between the Atlantic surface ridge and approaching remnants of Ida to the west. Because Ida is forecast to be a larger/stronger remnant cyclone… my forecast track in the longer range is bumped east… and also assumes Kate will be absorbed by Ida’s remnant cyclone by day 5.

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

0 Hr Position (0000Z Aug 31)… 40 mph maximum sustained wind tropical storm centered at 22.7N-50.9W

IOH 24 Hr Forecast (0000Z Sep 1)… 40 mph maximum sustained wind tropical storm centered at 26N-51.5W

IOH 48 Hr Forecast (0000Z Sep 2)… 45 mph maximum sustained wind tropical storm centered at 28.5N-55W

IOH 72 Hr Forecast (0000Z Sep 3)… 50 mph maximum sustained wind tropical storm centered east of Bermuda at 32N-59.5W

IOH 96 Hr Forecast (0000Z Sep 4)… 50 mph maximum sustained wind tropical storm centered at 36N-56W

IOH 120 Hr Forecast (0000Z Sep 5)…Absorbed by Ida’s remnant cyclone while located near 42N-53W


AREA OF INTEREST #1… The vigorous tropical wave of low pressure that has been over western Africa has arrived into the eastern tropical Atlantic. A low pressure spin is becoming increasingly defined near 10N-17.5W. Computer models have remained gung-ho on developing this wave as it moves into the eastern tropical Atlantic… therefore I am maintaining a tropical cyclone formation Forecast as outlined below. Although the wave will be aided by the low shear and upper outflow of the tropical Atlantic upper ridge… I have lowered the intensity forecast a bit in response to the global models showing a slower ramp up in the intensification… and also as the thunderstorm activity in the circulation of the wave is not as intense as 24 hours ago. However my intensity forecast still calls for a category 2 hurricane by day 5.


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 in the northwest Altantic as that trough slides east. Curiously the GFS has consistently shown an early northward turn toward this weakness while entangling this system with an adjacent tropical wave to the east… with the entanglement resulting in a slower west track that allows this system to fall north into the weakness instead of moving faster to the west and missing the weakness. The GFS also shows a stronger weakness that encourages an early north bend in track because it wants to develop the adjacent wave as the adjacent wave is swung northwest by this system. However the northwest track of the adjacent wave would take it toward cooler water and dry Saharan air…. and so I’m not buying the GFS scenario fully. However the distance between the adjacent wave and this system has decreased as the latest Satellite pics show the adjacent wave has accelerated westward into Western Africa while the low pressure spin of this system is consolidating a bit further East… so I think the GFS may be partially correct. As a result… I have made a compromise between the GFS and the other models… still showing a westward track over the next five days as the other models show but at the same time shifting my forecast track points more north and east.

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

0 Hr Position (0000Z Aug 31)… Tropical low pressure located offshore of western Africa at 10N-17.5W

IOH 24 Hr Forecast (0000Z Sep 1)… 30 mph maximum sustained wind tropical depression centered due south of the Republic of Cabo Verde Islands at 11N-22.2W

IOH 48 Hr Forecast (0000Z Sep 2)… 50 mph maximum sustained wind tropical storm centered southwest of the Republic of Cabo Verde Islands at 11.5N-26W

IOH 72 Hr Forecast (0000Z Sep 3)… 75 mph maximum sustained wind hurricane centered at 12.5N-30.5W

IOH 96 Hr Forecast (0000Z Sep 4)… 90 mph maximum sustained wind hurricane centered at 13.5N-35W

IOH 120 Hr Forecast (0000Z Sep 5)… 110 mph maximum sustained wind hurricane centered at 14.5N-40W


AREA OF INTEREST #2… An area of low surface pressure offshore of the US east coast has been left behind by the tail end of the cold front associated with the current northwest Atlantic frontal low. 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. However the eastern divergence zone of the other upper trough now approaching from eastern Canada may give this low pressure area what it needs to finally fire thunderstorms… in fact the thunderstorm activity has slightly increased between 0000Z and 0400Z. Plus the models shows the approaching upper trough not digging south into the upper ridging as the warm core upper ridging maintains strength from the surface warm southerly flow to be generated by the east side of Ida’s remnants… so wind shear associated with the incoming upper trough 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 3. However I have low development odds as none of the global models ever showed this system developing. The approaching Central Canada frontal low is expected to accelerate this system east-northeast out to sea.

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

IOH 24 Hr Outlook (0000Z Sep 1)… 10% chance of tropical cyclone formation (northwest Atlantic near 39N-67W)

IOH 48 Hr Outlook (0000Z Sep 2)… 10% chance of tropical cyclone formation (northwest Atlantic near 40.5N-59W)

IOH 72 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 a few days ago spawned what is now Tropical Storm Kate is currently inactive while in the eastern Caribbean Sea. 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 while 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 continued to produce thunderstorms downstream of the wave and over southern Caribbean water… and this wave could merge with that activity in the 2 to 4 day window. The only global model that shows this system developing is the CMC l… and it has now delayed its timeframe for showing development and has a weaker system… so I have lowered development odds to 20%… coming into agreement with the NHC Outlook at this time. By days 2 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. I have also adjusted the forecast positions in the Outlook below to the east due to the current position of the wave in the NHC TAFB surface analysis relative to the previous forecast. Based on the latest forecast track… interests in Belize and the Mexican Yucatan provinces should be aware of this system as it is expected to approach by this weekend.

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

IOH 24 Hr Outlook (0000Z Sep 1)…0% chance of tropical cyclone formation (eastern Caribbean Sea near 13N-67.5W)

IOH 48 Hr Outlook (0000Z Sep 2)…0% chance of tropical cyclone formation (central Caribbean Sea near 13.5N-72.5W)

IOH 72 Hr Outlook (0000Z Sep 3)…20% chance of tropical cyclone formation (central Caribbean Sea near 14.2N-77.5W)

IOH 96 Hr Outlook (0000Z Sep 4)…20% chance of tropical cyclone formation (western Caribbean Sea near 15.5N-82.5W)

IOH 120 Hr Outlook (0000Z Sep 5)… 20% chance of tropical cyclone formation (offshore of the Belize/Mexico border near 17.5N-87.5W)


...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 Depression Ida… transitions into a remnant low which strengthens to a frontal cyclone centered just offshore of Newfoundland at 120 hours.

**For Tropical Storm Kate… weakens to a remnant low near 25N-52W by 36 hours

**For area of interest #1… located at 18N-42W at 120 hours as a large hurricane

**For area of interest #2… no development shown

**For area of interest #3… consolidates into a tropical low in the Bay of Campeche offshore of Veracruz at 144 hours.

**Tail end of cold front driven by Ida’s remnant low evolves into a subtropical to tropical disturbance offshore of the southeast US by 120 hours


1200Z ECMWF Model Run…

**For Tropical Depression Ida… transitions into a remnant low which strengthens to a frontal cyclone making landfall at Nova Scotia at 120 hours.

**For Tropical Storm Kate… weakens to a remnant low near 24N-51W by 24 hours

**For area of interest #1… located at 17N-43W at 120 hours as a large hurricane

**For area of interest #2… no development shown

**For area of interest #3… no development shown


1800Z GFS Model Run...

**For Tropical Depression Ida… transitions into a remnant low which strengthens to an intense frontal cyclone centered between Newfoundland and Nova Scotia at 120 hours.

**For Tropical Storm Kate… weakens to a remnant low near 24N-52W by 27 hours

**For area of interest #1… located at 17N-37W at 120 hours as a compact hurricane

**For area of interest #2… no development shown

**For area of interest #3… no development shown

**Another tropical wave develops northeast of area of interest #1 after passing over the Republic of Cabo Verde Islands at 69 hours… located at 26N-31W at 120 hours as a weak tropical storm.


1800Z NAVGEM Model Run...

**For Tropical Depression Ida… transitions into a remnant frontal low supported by amplifying shortwave upper trough…remnant frontal low stalls over the Carolinas at 72 hours under an upper vortex that cuts-off from the south side of the amplifying upper trough… while whirling west under the upper vortex center where there is a lack of divergence the remnant low dissipates over northern Alabama at 108 hours

**For Tropical Storm Kate… weakens to a remnant trough near 34N-54.5W at 108 hours

**For area of interest #1… located at 16N-39.5W at 120 hours as a large tropical storm

**For area of interest #2… no development shown

**For area of interest #3… consolidates into a tropical low in the western Gulf of Mexico near 22.5N-93W at 150 hours.

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