*******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.**********
...FRIDAY AUGUST 12 2022 6:45 AM EDT...
While the eastern and central tropical Atlantic remain calm due to an outbreak of dry saharan air... attention turns to the western part of the Atlantic basin for potential tropical development as follows:
(1) A tropical low pressure area has developed in the northern Gulf of Mexico just offshore of Louisiana... see area of interest #15 section below for more information.
(2) The large upper trough and surface frontal system currently over eastern North America is heading into the western Atlantic. In about 72 hours (3 days)... models are in disagreement about whether or not this upper trough will leave behind an area of cut-off upper vorticity offsore of the southeastern United States. If this were to occurr... the eastern divergence zone of the upper vorticity...combined with the low shear due to the amplified nature of the upper vorticity... may allow for a subtropical or tropical disturbance between the United States east coast and Bermuda. On Thursday's 1200Z cycle of model runs the GFS hinted at this idea... and the current 0000Z cycle of models runs had the CMC hint a this idea. Any tropical or subtropical disturbance that does develop between Bermuda and the United States east coast will be short-lived while quickly becoming absorbed into a much larger non-tropical frontal low in the northwest Atlantic to develop with the support of the upper trough currently approaching from northern Canada. Not delcaring an area of interest for this situation at this time as models disagree on whether or not the required cut-off upper voriticty will be left behind or not.
New to this site this year... I will be sequentially numbering up areas of interest for possible Atlantic tropical development. In this scheme... will reset back to #1 at the start of next year (January 2023). The current area of interest in this blog post is designated #15 as I designated the other fourteen of this year in previous birdseye view posts on the home page. This scheme is to reduce confusion as Atlantic tropical activity increases during the peak of the hurricane season... when multiple simultaneous areas of interest begin and end which previously required shuffling around the area of interest numbers from update to update.
AREA OF INTEREST #15...As of Thursday afternoon and through the early morning hours of today... it appears a tropical area of low pressure with rotating cloud and thunderstorm bands has developed in the northern Gulf of Mexico just offshore of Louisiana. It appears a few subtle signatures in the atmosphere over the last few days have contributed to the development of this feature. First was the merger between an upper ridge cell in the northwestern Gulf of Mexico and the sprawling upper ridge over the central United States...with the merged upper ridge contributing to an upper outflow pattern across the northern Gulf of Mexico which helps keep surface pressures low. Further north and inland over the southeastern United States...the tail end of a slow moving surface front and trapped cut-off upper vorticity have been present over the last few days. The upper vorticity... which has recently merged with the current upper trough moving across eastern Canada... has also been recently sliding south toward the northern Gulf of Mexico due to the sprawling central United States upper ridge. Divergence ahead of the upper vorticity may have contributed to the lowering of surface pressures in the vicnity of the US Gulf coastal region while perhaps also recently sustaining the tail end of the aforementioned surface front. It is also possible that low-level lift ahead of the surface front also helped kick up the pulse of Thursday afternoon showers and thunderstorms across the northern Gulf of Mexico and US Gulf coastal region.
A focused low-level rotation in association with the new northern Gulf of Mexico tropical low pressure area is confirmed in the CIMSS 850 mb vorticity product (http://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=). Even though the thunderstorm activity generally relaxed Thursday night... as of this early morning showers and thunderstorms have continued to gradually increase on the east side of the tropical low. With these observations... I have declared this tropical low as an area of interest for further development on this blog... making this the fifteenth Atlantic tropical area of interest I have tracked this year. As of the 0000Z cycle the only major global model that shows the tropical low developing a defined surface spin is the NAVGEM. However the NAVGEM shows the surface spin develop further west of where current satellite animation shows the maximum spin...which reduces the steering effect of the Atlantic surface ridge such that the current Great Lakes surface ridge is allowed to push this system westward into the Texas coast. At this time I am considering the NAVGEM of having a westward bias... and in the forecast below I show an initially slow northwest track while this system remains trapped between the Atlantic and Great Lakes surface ridges. By 48 hours a faster northwest track... which takes this system into Louisiana... is shown as the current frontal low over the Dakotas slides east and erodes the Great Lakes ridge. I have low odds of tropical cyclone formation as close proximity to land may make conditions difficult for tropical cyclone formation... however I am starting with odds just above 10% (at 15%) due to the conitnually increasing patch of thunderstorms on the east side of the tropical low in recent hours. Regardless of tropical cyclone formation or not... the slow moving nature of this system may allow for heavy rains with flash flooding potential across Louisiana and southern Mississippi over the next day or so.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Aug 13)...15% chance of tropical cyclone formation (coast of south-central Louisiana near 29.2N-91.2W)
IOH 48 Hr Outlook (0600Z Aug 14)...0% chance of tropical cyclone formation (west-central Louisiana near 31.2N-93W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
0000Z (Aug 12) CMC Model Run...
**For area of interest #15...no development shown
**Surface low develops offshore of Georgia near 31N-78.5W at 54 hours... moves northeast and passes north of Bermuda at 114 hours where it becomes absorbed by large frontal low developing in northwest Atlantic
0000Z (Aug 12) ECMWF Model Run...
**For area of interest #15...no development shown
0000Z (Aug 12) GFS Model Run...
**For area of interest #15...no development shown
0000Z (Aug 12) NAVGEM Model Run...
**For area of interest #15...tropical surface low becomes defined offshore of southwestern Louisiana near 28.5N-93.5W at 18 hours... drifts west and makes landfall between Galveston Bay and Matagorda Bay on the Texas coast at 48 hours... dissipates over inland southern Texas by 72 hours.