*******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… TUESDAY MARCH 18 2025 7:15 PM EDT…
The pre-season area of interest… the surface cyclone northeast of the Lesser Antilles… has not undergone tropical development while increasing westerly shear has displaced any nearby shower and thunderstorm activity off to the east. This system is now continuing north west toward a developing frontal low offshore of the eastern US heading toward Bermuda which will absorb it. Meanwhile the Bermuda-area system is also not expected to develop tropical characteristics. My next birdseye view post on the Atlantic tropics will be when the hurricane season starts in June… or if another pre-season Atlantic tropical area of interest materializes before then.
...MONDAY MARCH 17 2025 3:32 PM EDT...
Temporarily resuming daily posts on the Atlantic tropics... before the official start of the Atlantic Hurricane Season in June... due to the National Hurricane Center declaring a pre-season tropical area of interest northeast of the Lesser Antilles islands. See area of interest #1 section below for details.
AREA OF INTEREST #1... March 13 to 17 Satellite sequence showing the progression of the leading upper trough/vortex that has spawned the area of interest northeast of the Lesser Antilles:
Over the last few days have been monitoring the progress of a leading small upper trough over the southeastern US and trailing major upper trough over the western US. From March 13 through today the leading upper trough entered the western Atlantic and settled into the open central Atlantic waters northeast of the Lesser Antilles. During this same timeframe the trailing upper trough produced a vigorous central/eastern North America surface frontal cyclone which was most notable for severe t-storms and tornadoes across a swath of the southeastern United States during this past weekend. Northward warm air transport ahead of the vigorous frontal cyclone has since built up a warm core upper ridge over the northwest Atlantic which in turn has caused the leading upper trough NE of the Lesser Antilles to amplify into a cut-off upper vortex. The increasing divergence on the east side of the amplifying upper feature has in turn produced a rapid-forming surface cyclone near 25N-55W which the NHC is watching for acquisition of tropical characteristics in the short-term. Sea surface temperatures in the region are 24 deg C... or about 1 deg C above the long-term average (https://www.nhc.noaa.gov/sst/). In the upper-levels the 200 mb layer of the upper vortex is positioned at a height of 1210 dekameters... would have preferred seeing colder upper air temps (heights closer to 1200 dekameters or lower) given that sea surface temps are below 26 deg C. However given that waters are almost 26 deg C perhaps there is just enough instability needed for some tropical activity... albeit on infrared satellite the system is not that impressive with only a few curved bands of showers/t-storms just north of the surface center.
Going forward the tail end of the vigorous trailing upper trough/surface front now emerging from eastern North America becomes a large cut-off deep-layer cyclone in the vicinity of Bermuda due to upstream warm core upper ridging building over the central US. The upper southwesterly flow ahead of Bermuda-area system kicks the overhead upper vortex overtop this area of interest off to the northeast... which should subject this area of interest (surface cyclone) to increased westerly shear less favorable for tropical development in the immediate wake of the departing parent upper vortex/trough in as soon as 24 hours. This will also cause this area of interest (surface cyclone) to begin weakening while no longer coupled to the eastern divergence zone of the parent upper vortex/trough. The weakening surface cyclone is also expected to turn northwest into the waters southeast of Bermuda while steered between the current central Atlantic surface ridge and developing Bermuda-area deep-layer cyclone... and eventually the weakening surface cyclone is absorbed into the Bermuda-area system. The surface layer of the Bermuda-area deep-layer cut-off cyclone is expected to be oblong in nature with multiple centers due to the oblong nature of its upper layer vortex which will have an elongated rather than focused upper divergence zone... and with a lack of a well-defined surface center the forecast Bermuda-area system is not expected to become another tropical area of interest.
Due to the above-mentioned unfavorable upper wind profile in as soon as 24 hours coupled with lackluster infrared satellite appearance of this system... assigning a 0% chance of subtropical cyclone formation for this area of interest as noted below.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
IOH 24 Hr Outlook (1800Z Mar 18)... 0% chance of subtropical cyclone formation (central Atlantic near 27.5N-59W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 12:20 PM EDT***********************
Formation chance through 48 hours... 10%
Formation chance through 7 days... 10%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
1200Z (Mar 17) CMC Model Run...
**For area of interest #1... While turning NW into the waters SE of Bermuda becomes quickly absorbed by frontal system moving offshore of eastern US by 30 hours.
0600Z (Mar 17) ECMWF Model Run...
**Not available at above-mentioned source
1200Z (Mar 17) GFS Model Run...
**For area of interest #1... While turning NW into the waters SE of Bermuda becomes quickly absorbed by frontal system moving offshore of eastern US by 30 hours.
0600Z (Mar 17) NAVGEM Model Run...
**For area of interest #1... Maintains a well-defined center with possible tropical character while positioned near 25N-56.5W through 24 hours... then through 42 hours turns north while quickly becoming absorbed by frontal system moving offshore of eastern US.
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