MY 2025 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #34

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

...WEDNESDAY JULY 9 2025 6:10 PM EDT...

For the tropical latitudes of the Atlantic basin... tropical development between Africa and the Lesser Antilles continues to be precluded by surges of dry Saharan air. Meanwhile 36 hours ago surface convergence on the north apex of a surface tropical wave of low pressure that had entered the eastern Pacific from Central America combined with upper divergence to the southeast of a retrograding upper vortex over the western Gulf of America combined to produce strong thunderstorms over Mexico's Isthmus of Tehuantepec. Since then the disturbance has drifted northwestward across the western Bay of Campeche and Veracruz while steered by the southwestern fringe of the Atlantic surface ridge... with the center of rotation of the remaining low-level cloud deck being inland over Veracruz which coincides with the position of a mid-level low that was left behind by the tropical wave and is confirmed in the CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/atlantic/movies/wg8vor4/wg8vor4_loop.html). The inland position means the disturbance cannot take advantage of the warm Bay of Campeche waters and anticyclonic outflow in the gap between the retrograding upper vortex which is now over east-central Mexico and second upper vortex to the east over the Caribbean. On the southeast edge of the low-level cloud deck is a surface trough in the central Bay of Campeche also left behind by the tropical wave. So far the surface trough has not developed any noteworthy cloud formations or thunderstorms... thus it is becoming increasingly likely that it doesn't have time to develop as by 48 hours the anticyclonic outflow becomes squashed out while the Caribbean upper vortex to the east continues to retrograde west and closes the gap between it and the Mexico upper vortex. Therefore not declaring an area of interest in the Bay of Campeche/ Veracruz region.

For the mid-latitudes of the Atlantic basin... the surface trough of low pressure which recently moved into the northwestern Bahamas remains positioned between a small upper vortex to the north (now currently near 31N-72W) and larger Caribbean upper vortex to the south. The gap between the two upper vortices has already re-increased as the northern one is already turning more northwest and away while it rounds the current northwest Atlantic upper ridge... this is allowing for the northwest Bahamas surface trough to develop increased thunderstorms thanks to the help of the upper anticyclonic outflow developing in the increased gap between the two upper vortices. Going forward the surface trough becomes quasi-stationary in the short-term due to weak steering currents between a weak surface front passing to the north and weakened west side of the steering Atlantic surface ridge. The weak surface front and weakening of the west nose of the steering Atlantic ridge is to be induced by the divergence zone of the upper trough now approaching from the Great Lakes/ eastern Canada... the upper trough is also expected to pull the small upper vortex further north and absorb it so it is no longer a factor in the region. In the longer range... the quasi-stationary northwest Bahamas/ Florida peninsula surface trough is likely to be ingested into the weak surface front which will be attached to the main surface frontal low that the upper trough eventually produces... with the weak surface front extended across the open northwest Atlantic and into the interior southeast US thanks to the divergence zone of a weak band of upper vorticity that is cut-off from the upper trough. Warm core anticyclonic upper ridging that spreads in from the eastern US... courtesy of warm southerly flow ahead of our next surface frontal system/ upper trough to move into central North America... is what separates the band of cool core upper vorticity from the first upper trough and then dissipates it... and the weak surface front has a high chance of being downgraded to a surface trough with no air mass contrasts on either side as it becomes embedded within the sprawling warm air mass... and it could take advantage of the warm core anticyclonic upper ridging to evolve into a tropical disturbance. Solutions from the GFS and CMC model runs that hint at tropical development are wide-ranging... therefore it is currently hard to pinpoint whether development occurs over the open northwest Atlantic (along the north wall of the warm Gulf stream waters) or closer to the United States mid-Atlantic or southeast coast... thus in this update cycle I am not declaring a tropical area of interest with a track forecast and probabilities of tropical cyclone formation. Should a better-defined surface circulation in the region develop in future satellite observations... and/ or computer models converge on a consistent solution... will be declaring a tropical area of interest in future updates.

...COMPUTER MODEL SUMMARY...

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

1200Z (Jul 9) CMC Model Run...

**Current Great Lakes/ eastern Canada upper trough continues east and drives a surface cold front into the northwestern Atlantic from the northeastern US by 54 hours... tail end of the surface front decays into a surface low offshore of the mid-Atlantic US through 66 hours which is positioned beneath upper ridging to the southwest of the upper trough... under force of the upper ridging the upper trough to the northeast dives south toward the surface low and it transitions to a frontal low (due to the cold air associated with the upper trough reaching one side of the low) by 102 hours located near 38N-65.5W and supported by split flow upper divergence between the southwest side of the upper trough and the flow around the upper ridging... in longer range the upper trough continues east which leaves the frontal low and its cold front attached to its west side to decay into a pair of surface lows near 39.8N-62W (open NW Atlantic) and 33.5N-74W (just southeast of Cape Hatteras North Carolina) with both surface lows festering under the upper ridging... by 168 hours the eastern of the two surface lows transitions into a frontal low southeast of Nova Scotia under the supportive eastern divergence zone of the next upper trough in the mid-latitudes breaking through the upper ridging from Atlantic Canada while the western of the two gains tropical characteristics under the outflow of the upper ridging and over the north wall of the Gulf stream while reaching 39.8N-65W

0000Z (Jul 9) ECMWF Model Run...

**No tropical development shown in the Atlantic basin over the next 168 hours (7 days)

1200Z (Jul 9) GFS Model Run...

**Current Great Lakes/ eastern Canada upper trough continues east and reaches Newfoundland by 84 hours where its southeastern divergence zone supports a main surface frontal low just southeast of Newfoundland with a trailing surface cold front attached to it and draped across the northwest Atlantic... at 96 hours a focused upper divergence zone develops at 36N-56W between the southwesterlies ahead of the upper trough and northerlies arcing across the eastern nose of adjacent northwest Atlantic upper ridging which results in a compact surface low along the front featuring tropical characteristics due to its location at the northeast end of the warm Gulf stream waters... the very compact tropical low then continues east to 36N-51.5W through 114 hours while moving in tandem with the upper trough and its main surface frontal low... by 129 hours while in the open north-central Atlantic the compact tropical low transitions back into a north-south elongated surface cold front attached to the main surface frontal low due to cooler waters and cold air pushed south by the back side of the main surface frontal low reaching one side of the remnant front... with the remnant surface cold front supported by the elongated southeastern divergence zone of the southward-digging cold core upper trough

**Through 57 hours the southwest part of Great Lakes/ eastern Canada upper trough separates and becomes a SW/NE tilted band of upper vorticity over the southeast US whose leading upper divergence zone helps to extend the surface cold front associated with the upper trough southwest across the northwest Atlantic and into the southeast US... the next surface front/ upper trough in the mid-latitude westerlies reaches central North America by 78 hours with the surface warm southerly flow ahead of the front dissipating the cool core SW/NE upper vorticity band over the SE US and replacing it with warm core upper ridging while the interior SE US portion of the surface cold front degenerates into a surface trough over North Carolina... in longer range the western upper convergence zone of the passing upper trough/ surface front from central North America builds a surface ridge to the northwest of the Carolina surface trough which steers the surface trough southwest into the eastern Gulf of America... by 168 hours the eastern Gulf surface trough transitions into a broad tropical low thriving under the outflow of warm core upper ridging associated with the warm air ahead of yet another surface frontal system/ upper trough moving into central North America.

1200Z (Jul 9) NAVGEM Model Run...

**No tropical development shown in the Atlantic basin over the next 168 hours (7 days)