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 #110

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


…UPDATE… TUESDAY SEPTEMBER 14 2021 2:52 AM EDT…

As of 2 AM EDT… the NHC has called the landfall of Hurricane Nicholas’s center on the Texas coast.. and based on Doppler radar the center is sliding east-northeast along the coast while located east of Bay City and heading toward Galveston. See the full update from 2:30 AM EDT below for more information on Nicholas and the rest of the Atlantic tropics.


...TUESDAY SEPTEMBER 14 2021 2:30 AM EDT...

The mid-September climatological peak of the Atlantic Hurricane Season is showing … with Hurricane Nicholas affecting southeast Texas and southern Louisiana… and four other areas of interest to watch for future development. Each system is detailed in its own section below.


TROPICAL STORM NICHOLAS (RECENTLY UPGRADED TO HURRICANE NICHOLAS)… The forecast track of Nicholas required adjustment last night when the surface center made a northward reformation into its sheared off thunderstorms… the updated forecast was in special update #109A on the home page of this site. Since then Nicholas has been on the northwest side of the upper ridge in the Gulf of Mexico where the shear direction was more southwesterly… pushing the thunderstorms toward the northeast of the center. Nicholas made a second center reformation to the northeast and into its the sheared off thunderstorms this morning (around 8:40 AM EDT)… but has still followed the forecast track from special update #109A while the center is nearing the Texas coast northeast of Corpus Christi and just east of Matagorda Bay… at Bay City. Therefore in the short-term my updated forecast track is the unchanged… showing Nicholas slowing down and turning more east in track while the storm is now tall enough to be dragged east by the upper westerlies on the north side of the Gulf upper ridge… against the southeast US surface ridge instead of freely flowing around the ridge. My longer term updated forecast track is adjusted to the east as the models forecast Nicholas to weaken and become more shallow from land interaction and shear induced by the upper westerlies… and yet through 48 hours still show Nicholas drifting slowly east against the southeast US surface ridge. One would think the shallower weakened circulation of Nicholas would decouple from the upper westerlies and be able to turn north around the surface ridge. This phenomenon in the model results is explained by the upper wind field developing a divergence zone near the Louisiana/Mississippi border as the upper westerly flow deforms with the approach of the frontal system/upper trough from central North America… and apparently the models see Nicholas’s remnants transitioning into a less tropical system supported by this upper divergence.


The intensity forecast from special update #109A also performed spot-on… as Nicholas was able to just recently become a 75 mph max sustained wind hurricane while the center is just about to move onto the Texas coast. Enablers for the intensification included enough coverage by the Gulf of Mexico upper ridge such that the shear was not too bad… and warm 30 deg C western Gulf of Mexico waters. Now that Nicholas is close to land and is entering stronger westerly shearing winds.. the hurricane is forecast to weaken and so my updated forecast intensity remains the same…

calling for a tropical depression by 24 hours and a remnant low by 48 hours.


With these forecast updates:

**Windy conditions are occurring in the Bay City and Houston/Galveston area… and have ended further southwest along the Texas coast. Stay sheltered indoors tonight as winds will continue for the next several hours as Nicholas slows down in track and takes time to weaken. If the eastward turn in track keeps the center of Nicholas toward the coast… the weakening could be prolonged which could allow gusty winds to reach the Beaumont Texas area and southwestern Louisiana. The onshore push of wind east of the center will contribute to coastal storm surge and sea swells in southeast Texas and southwest Louisiana over the next several hours.

**Heavy rainfall with flash flooding potential is a concern in southeast Texas… and with the more east and less north forecast track is also a concern across southern Louisiana. The risk is enhanced by Nicholas’s slowing track which will prolong the rainfall. Based on the latest radar… the risk for the most widespread flooding appears to be east of Houston and especially for southern Louisiana where the sheared off thunderstorms with heavy rain have arrived well in advance of Nicholas’s center… and it will continue to rain for several more hours until Nicholas’s center passes… although the Houston area should not let their guard down until the rains end there. Be mindful of things that will keep you safe from floodwater… such as avoiding driving into a water-covered roadway to prevent your vehicle from getting stuck which could result in drowning.


Here are the peak winds (mph) Nicholas has generated over the last several hours… as logged by National Weather Service Stations in the region:

**Corpus Christi TX… sustained 21… gust 35… 2:51 PM CDT

**Port Aransas TX… sustained 30… gust 40… 4:15 PM CDT

**Port Lavaca TX… sustained 38… gust 48… 7:22 PM CDT

**Bay City TX… sustained 45… gust 61… 11:35 PM CDT

**Bay City TX… sustained 38… gust 60… now

**Galveston TX… sustained 32… gust 51… now

**Houston TX… sustained 25… gust 33… now

**Beaumont TX… sustained 15… gust 23… now

**Lake Charles LA… sustained 14… now

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

0 Hr Position (1800Z Sep 13)… 65 mph maximum sustained wind tropical storm centered just offshore of Corpus Christi Texas at 27.4N-96.4W

IOH 24 Hr Forecast (1800Z Sep 14)… 35 mph maximum sustained wind tropical depression centered just east of Houston Texas at 30N-95W

IOH 48 Hr Forecast (1800Z Sep 15)… Remnant low centered on the northern Mississippi/Louisiana border at 32.3N-91W


AREA OF INTEREST #1… The shower and thunderstorm activity just north of the northeastern Caribbean Islands has lost its surface trough of low pressure… thus making this disturbance just an upper-level feature for now while the activity is being driven by the eastern divergence zone of the upper vortex in the region. The upper vortex is expected to drift west due to upper ridging to the north to be associated with the warm sector of the frontal system approaching from central North America… which will allow the thunderstorm to shift west toward the waters adjacent to the Bahamas. Models forecast a surface trough of low pressure to form in that region… and as the upper vortex fades while remaining cut-off from high-latitude cold air… the upper air pattern will become more anticyclonic with lower shear and upper outflow… thus more conducive for tropical development.


The forecast positions in the outlook below are initially based on the location of the eastern divergence zone of the upper vortex. By days 3 and 4 the frontal system from central North America will leave behind upper vorticity over the southeast US whose eastern divergence zone would create a narrow surface ridge weakness that this system would track northwest and northward into. By day 5… the next frontal system after that will push the upper vorticity toward this system and also create a surface ridge weakness in the northwest Atlantic which should attract this system on a northeast track.


Although the NHC has this system at 50% odds of development… I currently have a lower peak of 30% odds due to all models not showing development at any given time thus far. In addition by days 4 and 5 the forecast southeast US upper vorticity may shear this system. I plan to raise odds if this system gets better organized and/or if all/most models start to agree on developing this system. I taper odds of development down by day 5 as most models agree on transitioning this system to a more shared… more elongated… and less tropical low pressure area due to the approach of the upper vorticity… in other words becomes a system supported by the eastern divergence zone of the upper vorticity.


Coastal sea swells could reach the Bahamas and eastern US coast by days 3 to 5 if this system goes on to develop. Gusty winds and heavy rains may reach the North Carolina Outer Banks in about 4 days.

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

IOH 24 Hr Outlook (1800Z Sep 14)… 0% chance of tropical cyclone formation (north of the Dominican Republic and east of the eastern Bahamas near 21.5N-70W)

IOH 48 Hr Outlook (1800Z Sep 15)… 10% chance of tropical cyclone formation (northeast of the Bahamas near 25N-72.5W)

IOH 72 Hr Outlook (1800Z Sep 16)… 30% chance of tropical cyclone formation (offshore of the southeastern US near 30N-74W)

IOH 96 Hr Outlook (1800Z Sep 17)… 30% chance of tropical cyclone formation (southeast of Cape Hatteras North Carolina near 34N-74W)

IOH 120 Hr Outlook (1800Z Sep 18)… 10% chance of tropical cyclone formation (offshore of the northeastern US near 37.5N-70W)


AREA OF INTEREST #2… The tropical wave of low pressure that was over Western Africa has emerged into the eastern tropical Atlantic with a circular thunderstorm complex that features increasing banding features as of late. Due to the improving organization which suggests that dry Saharan air is not affecting this system thus far… favorable upper outflow and low shear of the stout tropical upper ridge in the region… and ongoing model support eventually showing development… I agree with the NHC’s high 80% odds of development by day 5. Forecast track in the 5-day window is due west into the central tropical Atlantic due to a lack of a notable surface ridge weakness.

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

IOH 24 Hr Outlook (1800Z Sep 14)… 50% chance of tropical cyclone formation (southeast of the Republic of Cabo Verde Islands near 11.5N-20W)

IOH 48 Hr Outlook (1800Z Sep 15)… 70% chance of tropical cyclone formation (south-southwest of the Republic of Cabo Verde Islands near 12N-25W)

IOH 72 Hr Outlook (1800Z Sep 16)… 80% chance of tropical cyclone formation (eastern tropical Atlantic near 12.5N-30W)

IOH 96 Hr Outlook (1800Z Sep 17)… 80% chance of tropical cyclone formation (eastern tropical Atlantic near 13N-35W)

IOH 120 Hr Outlook (1800Z Sep 18)… 80% chance of tropical cyclone formation (central tropical Atlantic near 13.5N-40W)


AREA OF INTEREST #3… The northeast Atlantic upper trough and surface frontal system has not acquired tropical characteristics while heading east for Portugal and Spain… and has been removed from the NHC outlook in the last 24 hours. The atmosphere has become more stable as the upper trough warms while remaining cut-off from high-latitude cold air. This is also my final statement on this system on this blog.

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

IOH 24 Hr Outlook (1800Z Sep 14)… 0% chance of subtropical cyclone formation (just offshore of southern Portugal near 38.5N-10W)


AREA OF INTEREST #4… Another tropical wave of low pressure featuring clusters of thunderstorm activity… currently over central Africa near 10N-6E… is Forecast to enter the eastern tropical Atlantic in 5 days. The ECMWF model has suggested the wave could develop with the stout presence of low shear and upper outflow supplied by the eastern tropical Atlantic upper ridge. The GFS has followed suit. Therefore I have introduced this wave as an area of interest… but have assigned low 10% odds of development at day 5 as tropical cyclone formation immediately offshore of Africa is generally rare. Odds could be increased in future updates once the 5-day window includes further offshore forecast points.

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

IOH 24 Hr Outlook (1800Z Sep 14)… 0% chance of tropical cyclone formation (western Africa near 10N-1E)

IOH 48 Hr Outlook (1800Z Sep 15)… 0% chance of tropical cyclone formation (western Africa near 10N-4W)

IOH 72 Hr Outlook (1800Z Sep 16)… 0% chance of tropical cyclone formation (western Africa near 10N-9W)

IOH 96 Hr Outlook (1800Z Sep 17)… 0% chance of tropical cyclone formation (vicinity of west coast of Africa near 10N-14W)

IOH 120 Hr Outlook (1800Z Sep 18)… 10% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-19W)


...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 Nicholas… Corpus Christi Texas landfall at 18 hours… weakens to a surface trough on the southeast Texas coast at 54 hours

**For area of interest #1… surface low develops offshore of North Carolina at 90 hours… strengthens as a non-tropical low which reaches the waters south of Cape Cod Massachusetts at 120 hours

**For area of interest #2… tropical wave amplifies into a tropical low pressure spin near 14.5N-48.5W at 120 hours

**For area of interest #3… makes landfall in Portugal at 42 hours and does not develop a tropical core

**For area of interest #4… no development shown


1200Z ECMWF Model Run...

**For Tropical Storm Nicholas… makes landfall between Corpus Christi and Galveston in next 24 hours… weakens to a surface trough on the southeast Texas coast by 72 hours

**For area of interest #1…strengthens as a non-tropical low offshore mid-Atlantic US at 120 hours

**For area of interest #2… located at 17.5N-50W as a compact tropical storm by 120 hours

**For area of interest #3… makes landfall between 24 and 48 hours in Portugal and does not develop a tropical core

**For area of interest #4… tropical wave departs Africa at 96 hours… tropical storm suggested just southeast of the Republic of Cabo Verde Islands by 120 hours


1200Z GFS Model Run...

**For Tropical Storm Nicholas… makes landfall between Corpus Christi and Galveston in next 18 hours…remnant low dissipates on northern Mississippi/Louisiana border at 84 hours

**For area of interest #1… possible tropical depression centered just offshore of Cape Hatteras North Carolina at 84 hours… tropical storm suggested southeast of Cape Cod Massachusetts by 120 hours.

** For area of interest #2… located at 11.5N-44W as a compact tropical storm by 120 hours

**For area of interest #3… makes landfall in Portugal at 36 hours and does not develop a tropical core

**For area of interest #4… tropical wave departs Africa at 96 hours… organizes into a tropical low south-southeast of the Republic of Cabo Verde Islands by 120 hours


1200Z NAVGEM Model Run...

**For Tropical Storm Nicholas... moves parallel to Texas coast and makes landfall at the Texas/Louisiana border at 54 hours… remnant low moves into northern Mississippi by 120 hours

**For area of interest #1…strengthens as a non-tropical low offshore of New Jersey at 120 hours

**For area of interest #2… large tropical depression centered at 13N-42W at 120 hours

**For area of interest #3… makes landfall in Portugal at 30 hours and does not develop a tropical core

**For area of interest #4… tropical wave departs Africa at 120 hours… organizes into broad tropical low in the long range

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