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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 #6

Updated: Apr 10, 2023

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


...SUNDAY APRIL 9 2023 2:06 AM EDT...

The potential for tropical development in the northern Gulf of Mexico remains low at present... 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 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. The upper trough of interest is currently positioned over the northwestern United States (Montana to Utah)... 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 amplified the jet stream pattern will be and hence how strong the surface low pressure will be. Individual global models are oscillating back and forth on the forecast strength of the event from run to run... within the computer model summary below the ECMWF and NAVGEM lead in forecast strength while the GFS has backed off (this is different from yesterday's update when the GFS was the leader in the forecast strength). A more amplified solution... where the upper trough becomes a cut-off upper vortex... will tend to favor tropical development through an increase in upper divergence on the east side of the upper vortex which will help in thunderstorm generation... reduction in wind shear... and the cold temps of the upper vortex helping to add instability... the boost in instability will be needed considering that northern Gulf of Mexico waters are currently running below 26 deg C (while at 24 deg C). I currently set odds of subtropical cyclone formation by day 4 at a low 10% as the models remain in disagreement on the strength of the forecast surface low pressure as discussed above... and as recent model solutions continue placing 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. Although upper air temps in the northern Gulf are expected to be on the cold side with 200 mb heights right at 1200 dekameters... would have preferred 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). The forecast track in the outlook below is nudged southeast over the previous to align toward the latest model consensus... and after the surface low pressure forms features a slow north hook between 72 and 96 hours while orbiting around the east side of the parent upper vortex. A faster and more north-northeast track is currently anticipated between 96 and 120 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. This track brings this system inland by 120 hours... as such development odds are dropped back to 0% for that timeframe.


Regarding impacts for the middle to later part of this upcoming week... due to the latest forecast track and anticipated westerly shear (which will keep the strongest weather towared the east side of the surface low pressure system) a general pattern of heavy rainfall... coastal surf/ rip currents... and breezy to gusty winds will be possible for southeastern Louisiana... 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. The strength of these impacts is somewhat uncertain at this time given the models are still in disagreement in the forecast strength of the surface low pressure system.

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

IOH 24 Hr Outlook (0000Z Apr 10)... 0% chance of subtropical cyclone formation (south-central Oklahoma near 34N-97.5W)

IOH 48 Hr Outlook (0000Z Apr 11)... 0% chance of subtropical cyclone formation (west-central Louisiana near 31N-93.8W)

IOH 72 Hr Outlook (0000Z Apr 12)... 0% chance of subtropical cyclone formation (just offshore of southeastern Louisiana near 28N-90.5W)

IOH 96 Hr Outlook (0000Z Apr 13)... 10% chance of subtropical cyclone formation (southeastern Louisiana near 29.2N-90W)

IOH 120 Hr Outlook (0000Z 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/)


1200Z (Apr 8) CMC Model Run...

**For area of interest #2... broad surface low pressure forms in the southeastern Gulf of Mexico near 24.5N-86W at 120 hours


1200Z (Apr 8) ECMWF Model Run...

**For area of interest #2... surface low forms in the north-central Gulf of Mexico near 27.5N-90.5W at 102 hours... surface low lifts north and makes landfall on the southeastern Louisiana coast at 126 hours.


1800Z (Apr 8) GFS Model Run...

**For area of interest #2... broad surface low forms in the central Gulf of Mexico near 25N-90W at 81 hours... surface low moves north-northwest and makes landfall on the south-central Louisiana coast at 99 hours... dissipates over west-central Louisiana by 120 hours.


1800Z (Apr 8) NAVGEM Model Run...

**For area of interest #2... strengthening broad surface low materializes in northeastern Gulf of Mexico near 27.5N-87W at 90 hours... makes landfall just east of the Alabama/Florida border at 102 hours... continues north-northwestward inland with the center reaching the Mississippi/ Alabama/ Tennesssee border at 120 hours.

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