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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 2023 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #7

*******Note that forecast 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 APRIL 10 2023 6:46 AM EDT...

Pre-season subtropical disturbance anticipated to materialize just offshore of southeastern Louisiana by Wednesday... however its potential for subtropical cyclone formation remains low as it is expected to lift northward and onshore relatively quickly. See area of interest #2 section below for more information.


As done on this site starting last year... I will be sequentially numbering up areas of interest for possible Atlantic tropical development throughout the year... resetting back to #1 at the start of each year. This scheme is so that each area of interest retains a numeric identity from update to update... which reduces confusion when simultaneous areas of interest begin and end when tropical activity increases during the Atlantic Hurricane Season. The current area of interest is tagged #2 as the first was tagged in late January (see earlier posts #1 through #4 on the home page of this site).


AREA OF INTEREST #2... Continuing to watch for possible tropical development in the northern Gulf of Mexico by mid-week. As is typical when dealing with pre-season development in the Atlantic basin... we look for a pattern of amplified upper ridges and upper troughs in the jet stream. The upper trough of interest is currently positioned over the central United States... and over the next 48 hours is poised to both dive southeast toward Louisiana and amplify in response to an equally amplifying upstream upper ridge to its northwest. The amplifying upper ridge (associated with a warm air mass) is already beginning to gain footing over the western US due to northward warm air transport ahead of a broad and amplified northeastern Paicifc upper trough/surface frontal cyclone pushing into western Canada.


Concerning the amplifying upper trough energy that heads into Louisiana... models agree that the jet stream pattern mentioned above will be amplified enough to allow the Louisiana upper trough to amplify into a cut-off upper vortex. The southeastern divergence zone of the upper vortex by Wednesday is expected to lower surface pressures just offshore of or along the southeastern Lousiana coast... with whatever low pressure system that forms lifting northward and inland not long after its formation while it orbits the east side of the upper vortex. A faster and more north-northeast track is currently anticipated between 72 and 96 hours as the blocking warm deep-layer ridge to approach from the western/central US becomes eroded from the approach of the amplified upper trough energy from the northeastern Pacific. At this point the models have converged on a more compact upper vortex positioned further northwest over Louisiana... because my previous forecast track was in line with such a solution my updated one below is unchanged. This also means subtropical cyclone formation odds remain low as the emerging disturbance will have little time over water... therefore my peak odds of formation remain at a low 10%. Other factors that keep development odds low include the position of the upper vortex center over land instead of water... which will allow the south side of the upper vortex to impart some westerly shear over water where the disturbance would be trying to develop... and the 24 deg C water temperatures in the northern Gulf which are below the typical 26+ deg C threshold for tropical development. Although the cold temps of the upper vortex may help aid in generating instability as indicated by forecast 200 mb heights being right at 1200 dekameters... would like to have seen even colder temperatures (lower heights) for more confidence in tropical development given the below-26 deg C sea surface temperature environment.


Regarding impacts for the Wednesday/Thursday timeframe... given that the forecast track confidence is increasing we can narrow down the impact zone a little more to southeastern Louisiana... southern Mississippi... southern Alabama... and the western Florida panhandle which will primarily see enhanced rainfall. Some coastal surf and breezy winds will only be possible... particularly toward the western areas of the impact zone... if the subtropical disturbance manages to ramp up relatively quickly during its short time over water as suggested for example by this past 0000Z ECMWF model run (see model summary section below for more info on that run and other recent global model runs).

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

IOH 24 Hr Outlook (0600Z Apr 11)... 0% chance of subtropical cyclone formation (west-central Louisiana near 31N-93.8W)

IOH 48 Hr Outlook (0600Z Apr 12)... 0% chance of subtropical cyclone formation (just offshore of southeastern Louisiana near 28N-90.5W)

IOH 72 Hr Outlook (0600Z Apr 13)... 10% chance of subtropical cyclone formation (southeastern Louisiana near 29.2N-90W)

IOH 96 Hr Outlook (0600Z Apr 14)... 0% chance of subtropical cyclone formation (Mississippi/ Alabama border near 32N-88.5W)


...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)


0000Z (Apr 10) CMC Model Run...

**For area of interest #2... broad surface low pressure forms in the north-central Gulf of Mexico near 27N-90.5W at 72 hours... moves northeast and makes landfall just east of the Florida/Alabama border at 108 hours... dissipates over southern Alabama at 114 hours.


0000Z (Apr 10) ECMWF Model Run...

**For area of interest #2... surface low forms just offshore of south-central Louisiana at 28.5N-91.5W at 66 hours... while strengthening the surface low lifts north and makes landfall on the south-central Louisiana coast at 78 hours... dissipates just west of the northern Louisiana/Mississippi border at 96 hours


0000Z (Apr 10) GFS Model Run...

**For area of interest #2... surface trough forms on the southeastern Louisiana coast at 72 hours... moves west-northwest across Louisiana while dissipating through 96 hours.


0000Z (Apr 10) NAVGEM Model Run...

**For area of interest #2... broad surface low forms offshore of southeastern Louisiana near 27.5N-90W at 72 hours... makes landfall on the southeastern Louisiana coast at 84 hours... while continuing north dissipates over northern Mississippi at 108 hours.

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