*******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.**********
...TUESDAY MAY 30 2023 11:55 PM EDT...
Disturbance now being monitored for tropical cyclone formation materializes in the central Gulf of Mexico while supported by upper vorticity in the region... as it shifts eastward the disturbance is primarily expected to bring increasing rainfall to south Florida and the northwestern Bahamas through Friday. See area of interest #5 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 #5 as the first four were assigned in earlier birdseye view posts on this site.
AREA OF INTEREST #5... Hovmoller diagram showing the progression of the upper trough energy (May 29 to 30) that has recently triggered a tropical disturbance in the central Gulf of Mexico(https://www.nhc.noaa.gov/tafb_latest/gehov3latest.gif). The yellow oval represents the position of the upper trough energy in each satellite frame:
The disturbance that is now in progress in the central Gulf of Mexico is traced to a southern piece of upper trough energy from the western US that was able to slide eastward into the Gulf... to the south of the blocking upper ridge that has been over the Great Lakes/eastern North America... while the remainder of upper trough energy over the western US remains trapped due to the blocking upper ridge. Throughout the morning and afternoon hours of Tuesday... concentrated and somewhat organized thunderstorm activity developed in the central Gulf due to eastern divergence zone of the upper trough energy now in the Gulf. The CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=) over the last 12 hours has also shown the rapid formation of a circular mid-level low pressure rotation due north of the Yucatan peninsula (near 23.5N-87.5W). The ASCAT-C descending pass of surface winds (https://manati.star.nesdis.noaa.gov/datasets/ASCATCData.php) did miss the western half of the disturbance... however data pertaining the eastern half of the system also suggests increasing surface low pressure rotation to the north of the Yucatan. This new low-level low pressure system is in a sheared state as the thunderstorm activity has since relaxed... with the remaining comma-shaped cloud deck displaced to the northeast of the surface and mid-level rotation. Despite this... the National Hurricane Center since 2 PM EDT has begun to mention this area of interest in their tropical weather outlook to begin issuing odds of tropical cyclone formation. This is likely responsive to the above observations of a quickly-forming low-level low pressure system and the ECMWF model since 0000Z last night suggesting the development of a bonafide low-level low pressure system that heads toward south Florida from the central Gulf of Mexico.
The blocking warm core upper ridge over eastern North America over the last few days has been eroded by the passage of the high-latitude upper trough that has recently pivoted into the northwest Atlantic. Going forward the blocking ridge is expected to re-amplify and retrograde westward toward the central US due to ongoing northward warm air transport over the central US... caused by the flow due east of the broad field of low surface pressures over the western US being induced by the trapped western US upper trough energy. Over the next 24 hours the re-amplification of the blocking ridge will induce adjacent amplification of the current central Gulf of Mexico upper trough energy into an upper vortex... with increased upper divergence and lower shear on the east side of the upper vortex further supporting the low-level low pressure system and potentially allowing for its tropical development. By 48+ hours... the Gulf of Mexico upper vortex is forecast to merge with upper vorticity that has been trapped over the southeastern US and also a high-latitude upper trough from central Canada diving southeastward around the blocking ridge... with the merger resulting in a southwest-northeast tilted upper trough due to the initial position of each of the elements in the merger. The tilt direction will result in increasing westerly shear over the low-level low pressure area as it moves eastward from the central Gulf and toward the Florida peninsula and western Bahamas... with the tilted upper trough also featuring an elongated eastern divergence zone that will equally elongate and broaden the low-level low pressure system. Therefore in general conditions appear most favorable for tropical cyclone formation in the short-term... with longer-term conditions becoming more hostile as the low pressure area moves east under increasing westerly shear and as it also loses a well-defined center needed for focusing thunderstorms and tropical development as it becomes more elongated. The models are split into two camps regarding the merged tilted upper trough due to some disagreement on the exact evolution of the adjacent re-amplifying blocking upper ridge over North America... with the GFS and NAVGEM not showing much development of this area of interest while trending with a lower-amplitude and more titled upper trough... and the ECMWF and CMC showing a more bonafide surface low pressure area materializing while featuirng a less titled and higher amplitude upper trough with lower shear and more upper divergence on its east side. However even with the more bonafide ECMWF-CMC camp... it is not clear that this system would qualify for tropical cyclone status as the strengthening surface low pressure area also loses a well-defined center needed for cyclone formation while becoming elongated due to the mechanisms discussed above.
I agree with the NHC outlook on a low peak 20% odds of tropical cyclone formation due to the initally sheared state of this system and that it will only have a narrow window of lowering shear to last only the next 24 hours as discussed in the prior paragraph. Peak odds above 10% also seems like a good suggestion given the quick development of a well-defined low-level low pressure area in the CIMSS and ASCAT products. Odds higher than 20% do not seem warranted at this time as not all major global models (such as the current GFS-NAVGEM camp) agree on development. The difference in my outlook below... relative to the NHC... is on issuing the peak 20% odds in the shorter term as the analysis in the previous outlook suggests the best development conditions for only the next 24 hours. Regarding impacts... clusters of thunderstorms and heavy rainfall are currently in progress across the northwest Caribbean... Cuba... the Bahamas... and the western Atlantic due to upper divergence ahead of the current Gulf of Mexico and southeastern US upper vorticity. Through Friday... the periods of heavy rainfall activity and possible flash flooding will transfer north... primarily covering the northwestern Bahamas and southern Florida peninsula... in alignment with the position of the forecast tilted upper trough's eastern divergence zone expected to materialize in the region in the longer term. It is not certain at this time if gusty winds will occur for the northwestern Bahamas for Friday/Saturday as not all models agree with the more vigorous ECMWF solution.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Jun 1)... 20% chance of tropical cyclone formation (eastern Gulf of Mexico near 25N-85W)
IOH 48 Hr Outlook (0000Z Jun 2)... 10% chance of tropical cyclone formation (eastern Gulf of Mexico near 25N-85W)
IOH 72 Hr Outlook (0000Z Jun 3)... 0% chance of tropical cyclone formation (central Florida peninsula near 26.5N-81.8W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours...10%
Formation chance through 7 days (168 hours)...20%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (May 30) CMC Model Run...
**For area of interest #5... mid-level circulation currently in central Gulf of Mexico shifts east and evolves into a broad surface low when it reaches the southern Florida peninsula through 84 hours... broad surface low continues east into the northwestern Bahamas through 120 hours and loses identity along cold front of a developing frontal low to the northeast through 138 hours.
1200Z (May 30) ECMWF Model Run...
**For area of interest #5... mid-level circulation currently in the central Gulf of Mexico gradually develops a broad surface low near 25N-87W through 60 hours... broad surface low shifts east and crosses the southern Florida peninsula through 108 hours... center of the strengthening broad surface low passes just north of the western Bahamas through 120 hours... broad surface low transitions into elongated frontal cyclone in the western Atlantic near 30.5N-73.5W through 138 hours... frontal cyclone passes just north of Bermuda by 156 hours and merges with competing frontal cyclone to the northeast shortly thereafter.
1800Z (May 30) GFS Model Run...
**For area of interest #5... no tropical cyclone formation forecast
1800Z (May 30) NAVGEM Model Run...
**For area of interest #5... no tropical cyclone formation forecast