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 #109A (Special Update)

*******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…MONDAY SEPTEMBER 13 2021 8:40 AM EDT...

Left… Satellite image of Tropical Storm Nicholas taken at 1216Z. Right… Doppler Radar taken at the same time…red plus and arrow mark the position and short-term motion observed with the surface center:

Regarding Tropical Storm Nicholas… Doppler radar showed the spiral center nearing the coast at the Texas/Mexico border while continuing north-northwest… and some breezy northerly gusts at Brownsville and Port Mansfield confirmed this. Meanwhile the heaviest rainfall and thunderstorms are mainly east and offshore of the surface center due to upper southwesterly flow generated by the northwest side of the upper ridge in the Gulf of Mexico. Most recently… the spiral center on radar has taken a northeast turn which could indicate that a mid-level center buried in the thunderstorms is forcing the surface center offshore… or that another surface center is forming. Either way… the shift in the surface center’s track indicates winds and rainfall South of Corpus Christi are not likely to increase from currently levels. Nicholas currently has 60 mph max sustained winds… and could strengthen further to a hurricane later today if indeed the surface center relocates into the strongest thunderstorms. Landfall is still likely on the Texas coast near or to the northeast of Corpus Christi tonight… for more info on expected impacts and timing… see update below from 1:32 AM EDT.


Here are some of the latest National Weather Service Station observations of wind (mph):

**Brownsville TX… sustained 13… gust 22… now

**Port Mansfield TX… sustained 12… gust 23… 4:52 AM CDT

**Corpus Christ TX… sustained 9 (now)


...MONDAY SEPTEMBER 13 2021 1:32 AM EDT...

Satellite image of Tropical Storm Nicholas as of 0356Z. Yellow plus marks the position of the previous surface center of Nicholas… red plus marks the position of a more recent surface center found by aircraft reconnaissance:

Satellite imagery shows that Tropical Storm Nicholas fired a strong thunderstorm complex north of its 11 PM EDT surface center fix… and Doppler radar showed a well-defined spiral center in the complex moving north-northwest. Aircraft recon data (https://www.tropicaltidbits.com/recon/#AF305-0214A-NICHOLAS) then showed a new surface center notably to the north at 24.2N-96.2W… coincident with the spiral center on Doppler radar. As of 12:30 AM EDT… the National Hurricane Center officially announced the north reformation of the center. This special update is to also update my forecast for Nicholas given the center reformation. It should be noted that Nicholas had a broad center as sometimes seen in new tropical storms… often times when shear displaces the thunderstorms from the broad center a new tighter center can re-form toward the sheared off thunderstorm activity… especially if that activity releases enough latent heat of condensation to locally warm the air and thus make the air column taller… making a local upper-level high pressure ridge

that produces outflow to lower the surface pressure for a new surface center to form. This is what has happened with Nicholas.


Given the new center on radar is seen having a west angle in its north track… my updated track forecast for the next 24 hours brings Nicholas close to the Texas coast between Brownsville and Corpus Christi… with a landfall point just northeast of Corpus Christi. Curiously the 18Z GFS model run seemed to show an initially broad center… followed by a north reformation and ramping up of Nicholas’s intensity as we have just seen… and also agrees with a similar landfall point. The 18Z GFS also shows similar forecast positions to my previous forecast in full update #109… the only difference being that Nicholas arrives to those points sooner due to the northward reformation. Therefore my longer range updated forecast track is the same as previous… except Nicholas arrives to the forecast points 18 hours sooner. This means in 24 to 48 hours Nicholas is still forecast to slow down in track while reaching upper westerly flow on the north side of the Gulf of Mexico upper ridging that will push the storm against the southeast US surface ridge instead of letting the storm freely flow around the ridge. Between 48 and 72 hours I assume Nicholas will weaken from land interaction… allowing it to become shallower… decouple from the upper westerlies… and more freely flow north on the west side of the surface ridge.

Regarding intensity… I still forecast a category 1 hurricane landfall… but just slightly weaker as the updated storm position and west angle in the storm’s north track on radar will keep the center closer to shore and also bring the center to land a little quicker. Factors that will facilitate strengthening is the Gulf upper ridge trying to expand over Nicholas which may lower the shear and help the storm’s upper outflow… and also warm 30 deg C water.


With these forecast updates:

**The potential for gusty winds and heavy rain on the south Texas coastal region… between Brownsville and Corpus Christi… has increased… and could arrive soon as we progress through the early morning hours. Coastal sea swells are also likely as Nicholas strengthens further and just offshore.

**Preparations for tropical storm to hurricane force conditions from Corpus Christi/Matagorda Bay all the way toward the Texas/Louisiana border should now be finishing by late morning… impacts to arrive sooner and by tonight and into Tuesday. Preparations should include relocating further inland if you live in an area prone to coastal storm surge. Heavy rainfall with flash flooding potential is a concern in this region… and also inland over eastern Texas and western Louisiana… especially as Nicholas is expected to slow down as discussed above which will prolong the rainfall and potentially make widespread and life threatening flash flooding. The rainfall flooding could be similar to what has been seen in this region in recent storms such as Harvey 2017 and Imelda 2019. 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.

**Southwestern Louisiana may see tropical storm conditions by late Tuesday… especially if the northeast track keeps Nicholas close to shore which would allow it to maintain strength.

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

0 Hr Position (0000Z Sep 13)… 50 mph maximum sustained wind tropical storm centered in the western Gulf of Mexico at 24.8N-96.3W

IOH 24 Hr Forecast (0000Z Sep 14)… 75 mph maximum sustained wind hurricane centered on the Texas coast just northeast of Corpus Christi at 28N-97W

IOH 48 Hr Forecast (0000Z Sep 15)…35 mph maximum sustained wind tropical depression centered on the southern Texas/Louisiana border at 30.5N-94W

IOH 72 Hr Forecast (0000Z Sep 16)…Remnant low centered on the Louisiana/Arkansas border at 32.7N-93W


For more information on the rest of the Atlantic tropics… refer to full update #109 available on the home page of this site.

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