MY 2023 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #5
Updated: Apr 9
*******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.**********
...FRIDAY APRIL 7 2023 10:30 PM EDT...
More reliable GFS and ECMWF models suggesting some potential for subtropical development in the northern Gulf of Mexico by the middle of this upcoming week... therefore temporarily resuming daily birdseye view posts on the Atlantic tropics even though hurricane season does not officially start until June 1st. 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 Atlanitc 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... Pre-season tropical development possible in the northern Gulf of Mexico by the middle of this upcoming 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. Per the latest model runs... the upper trough of interest is currently positioned over the northwestern corner of the United States... and in the days ahead is poised to both dive southeast toward the northern Gulf of Mexico and amplify in response to an equally amplifying upstream upper ridge to its northwest. The amplifying upper ridge (associated with a warm air mass) will gain footing over the western US due to northward warm air transport ahead of a series of northeastern Pacific/western Canada frontal cyclones to be generated by the eastern divergence zone of amplified northeastern Pacific upper troughing.
Concerning the amplifying upper trough energy that heads into the northern Gulf of Mexico (by the middle of this upcoming week)... the eastern divergence zone of that energy will trigger a broad surface low pressure area in the northern Gulf of Mexico... but the question remains as to how strong the surface low pressure will be. The recent and more aggressive GFS model run shows a more amplified jet stream pattern resulting in a stronger surface low pressure while the other models have a less amplified jet stream pattern and equally weaker surface low pressure in their presentation. The GFS solution calls for the upper trough to amplify into a cut-off upper vortex located just inland from the northern US Gulf coast which will tend to reduce wind shear in the region needed for tropical development. Although water temperatures in the northern Gulf are below the typical 26 deg C threshold for tropical development (currently running around 24 deg C)... cold temperatures provided by the upper vortex may aid in developing instability... and the eastern divergence zone of the upper trough/vortex will also help in generating thunderstorm activity. I currently set odds of subtropical cyclone formation by day 5 at a low 10% as the models do not yet agree on the amplitude of the jet stream pattern which will make or break the potential for subtropical development as discussed above... and as the aggressive GFS solution places the center of the eventual upper vortex over land instead of water which would still allow for some westerly vertical shear counter-productive to tropical developemnt. Upper air temps in the northern Gulf are expected to be on the cold side with 200 mb heights right at 1200 dekameters... however would have liked to see colder temps (lower heights) than this for more confidence in subtropical development (given that sea-surface temps are below 26 deg C in the region).
Regarding impacts... the general forecast pattern supports a warm deep-layer ridge approaching from the western/central US while a surface low pressure area gains prominence in the Gulf of Mexico by the middle of the upcoming week. If the pressure gradient between the ridge and surface low becomes strong enough to generate widespread easterly surface winds... sea swells/rip currents could be widespread across the northern Gulf of Mexico coastal region from Texas all the way to the Florida panhandle. Westerly shear will tend to keep the inclement weather (rain... etc...) toward the east side of the surface low pressure area... over southeastern Lousiana... southern Mississippi... southern Alabama... and the Florida panhandle. Keep in mind these impacts are possible even if this system becomes a broad/disorganized subtropical low instead of a subtropical cyclone. Beyond day 5 (toward the later part of next week)... the most likely scenario is for the deep-layer ridge over the western/central US to be broken down as the northeastern Pacific upper trough energy finally moves in... with this energy helping to scoop what remains of this system northeastward into further interior portions of the southeastern US.
IOH 24 Hr Outlook (0000Z Apr 9)... 0% chance of subtropical cyclone formation (central Colorado near 39.5N-105W)
IOH 48 Hr Outlook (0000Z Apr 10)... 0% chance of subtropical cyclone formation (central Oklahoma near 35N-97.5W)
IOH 72 Hr Outlook (0000Z Apr 11)... 0% chance of subtropical cyclone formation (northwestern Louisiana near 31.5N-93.8W)
IOH 96 Hr Outlook (0000Z Apr 12)... 0% chance of subtropical cyclone formation (just offshore of south-central Louisiana near 29N-92W)
IOH 120 Hr Outlook (0000Z Apr 13)... 10% chance of subtropical cyclone formation (just offshore of southeastern Louisiana near 29N-89W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Apr 7) CMC Model Run...
**For area of interest #2... no development shown
1200Z (Apr 7) ECMWF Model Run...
**For area of interest #2... broad surface low pressure forms in the central Gulf of Mexico near 26N-91.5W at 120 hours.
1800Z (Apr 7) GFS Model Run...
**For area of interest #2... broad surface low pressure forms offshore of Louisiana near 28.5N-92.5W at 90 hours... moves east-southeast while developing into a potential subtropical cyclone near 26N-90W by 120 hours
1200Z (Apr 7) NAVGEM Model Run...
**For area of interest #2... broad surface low forms just offshore of southeastern Lousiana near 28N-90W at 120 hours