*******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 JUNE 21 2024 3:30 PM EDT...
See area of interest #6 section below for an update on the small tropical low currently heading for the Florida/Georgia border region from the western Atlantic. See area of interest #7 section below for information on the gyre of low pressure that has materialized over northwestern Central America... which is forecast to head northwestward toward the western Gulf of Mexico where it may potentially develop further.
Noting a band of upper vorticity is forecast to settle across the Gulf of Mexico in the days ahead... more information on that is also in the area of interest #7 section. It is possible that an area of divergence between this upper vorticity band and currently-blooming tropical upper ridge cell expanding from the Caribbean could trigger yet another area of disturbed weather in the region of Central America in the days ahead... in wake of area of interest #7. Long-term (through day 7) the upper winds may then become more conducive for tropical development as the tropical upper ridge cell and its supporting outflow expands in the wake of the decaying upper vorticity band. Yet another disturbance in this region would be a concern for rainfall flooding for western Central America and southeastern Mexico as Alberto and area of interest #7 have already saturated the grounds in this region. However have not declared another tropical area of interest for this region as of this writing as not all models are in agreement on this scenario.
Elsewhere... upper winds in the eastern and central tropical Atlantic (between Africa and the Lesser Antilles) will remain favorable for tropical activity over the next few days due to low shear and outflow provided by the tropical upper ridge axis in the region. However the tropical waves of low pressure passing through the region are not developing... and are not forecast to develop through day 7... due to ongoing outbreaks of dry Saharan air kicked up by the waves when they depart Africa.
AREA OF INTEREST #6... As stated in special update #22A overnight (https://www.infohurricanes.com/post/my-2024-atlantic-hurricane-season-birdseye-view-post-22a-special-update)... the compact western Atlantic tropical low pressure swirl heading west-northwest toward the southeastern United States shoreline re-organized further north and is closing in on the Florida/Georgia border region while continuing to be pushed by the large-scale surface ridging to the north. Throughout the morning aircraft reconaissance has been investigating this circulation... and although recon has spotted a closed surface circulation with 35 mph maximum sustained winds the NHC has not upgraded this system to a tropical depression as the associated small thunderstorm core is beginning to become sheared off to the south of the swirl center... thanks to the approaching upper vortex to the northeast. However the NHC also states that any small increase in the organization of the thunderstorm activity (for instance a new burst of thunderstorms that covers the swirl center) could result in an upgrade to tropical depression status. Because this system is heading at a good clip to the west-northwest and the shearing upper vortex to the northeast is having to chase it... I do not expect the northerly shear levels over this system to appreciably increase before this system makes landfall and I currently forecast this system to make landfall at the Florida/Georgia border region as a tropical depression by this evening. Regardless of whether or not this system is classified as a tropical depression by the time it makes landfall... expect a short-lived period of gusty winds and heavy rainfall... most likely for the northeast corner of Florida. The chances for a burst of inclement weather for the southeast corner of Georgia are lower due to the aforementioned northerly shear which is keeping the strongest thunderstorms south of center.
I plan this to be my final update on this area of interest on this blog as it is forecast to be a dissipating surface trough over the southeastern United States by the time I do my next full update over the weekend. I may carry update statements on this system on the home page bulletins of this site or in special update posts wihtin the next 24 hours.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Jun 21)... 35 mph maximum sustained wind tropical low centered offshore of the Florida/Georgia border 30.5N-79.5W
IOH 12 Hr Forecast (0000Z Jun 22)... 35 mph maximum sustained wind tropical depression centered on the southeastern United States coast... over the Florida/Georgia border... at 30.8N-81.5W
IOH 24 Hr Forecast (1200Z Jun 22)... Dissipating surface trough over south-central Georgia located near 31.2N-83W
*****National Hurricane Center (hurricanes.gov) official outlook as of 10:35 AM EDT*************************
Formation chance through 48 hours... 60%
Formation chance through 7 days... 60%
AREA OF INTEREST #7... A surface trough of low pressure persists across the Bay of Campeche... northwestern Central America... and western Caribbean waters offshore of Honduras. Based on the developing curvature of the regional thunderstorm bands... the area of maximum spin along the surface trough has materialized over northern Guatemala and Belize which is confirmed by the CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=atlantic&sat=wg8&prod=vor&zoom=&time=). This is further west than my previous forecast... the updated forecast in my outlook below is adjusted accordingly. The prognosis as to why the area of maximum spin has materialized further west can be seen in the latest upper-level wind charts... specifically in the upper-levels there is an upper vortex that has been retrograding southwestward across the Gulf of Mexico. The upper vortex is weakening its from prolonged isolation from high-latitude cold air as previous model runs suggested... however the vortex is actually further west and weaker/smaller than previous model projections. This has allowed the area of maximal upper divergence between the east side of the decaying upper vortex and northwest side of the blooming Caribbean upper ridge cell (developing in the wake of the decaying upper vortex) to be positioned further west... hence dropping surface pressures at a further west location. As to why the upper vortex weakened faster than expected? Perhaps due to the tremendous thunderstorms and latent heat release this area of interest was producing across the western Caribbean and western Central America Thursday evening as noted in special update #22A (https://www.infohurricanes.com/post/my-2024-atlantic-hurricane-season-birdseye-view-post-22a-special-update) which helped to punch out the cold core upper vortex.
Forecast track is initially west-northwest due to the same steering surface ridge pushing area of interest #6... followed by a slow northward turn across the western Gulf of Mexico once the ridge erodes ahead of a pair of surface frontal systems to eject from western North America. The longer-term forecast track has a slow northward speed as the frontal systems pass well to the north instead of nearby. I have raised my peak odds of tropical cyclone formation to 40% as this system is better-organized compared to yesterday while now featuring curvature in the thunderstorm bands... and the westward-adjusted forecast track allows this system to enter the Gulf of Mexico sooner and before the disrputing upper vorticity currently northeast of AOI #6 surges into the Gulf as an east-west band. I have not picked odds higher than 40% as this system has a broad circulation and will need time to develop a better-defined center necessary for cyclone status... which may not happen before the disrputive upper vorticity band enters the picture. Note that any recent model runs that do develop this system... such as the GFS and CMC runs posted in the model summary section below... have the cyclone weaken while still over water (before landfall) due to the arrival of the upper vorticity band. For 72+ hours... I lower odds of tropical cyclone formation below the 40% peak... and hold on to this disturbance through 120 hours as their is a possiblity of this system hanging on as the upper vorticity band fades from prolonged isolation from high-latitude cold air... which could allow it to take longer-term advantage of low shear/outflow on the southeast side of the hot air mass upper ridge cell forecast to persist in the vicinity of Texas over the next several days. My odds of development for the longer-range are at a low 20% as the models do not currently show this idea at this time.
Regardless of tropical cyclone formation or not... the main takeaway for this area of interest is that it could produce heavy rainfall with flash flooding potential across western Central America and southeastern Mexico over the next couple of days. The flooding risk here is enhanced as what was the pre-Alberto circulation recently saturated the grounds in this region.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Jun 22)... 15% chance of tropical cyclone formation (southwest coast of the Yucatan peninsula near 19N-91W)
IOH 48 Hr Outlook (1200Z Jun 23)... 40% chance of tropical cyclone formation (southwestern Gulf of Mexico near 21.5N-93W)
IOH 72 Hr Outlook (1200Z Jun 24)... 20% chance of tropical cyclone formation (southwestern Gulf of Mexico near 23N-95W)
IOH 96 Hr Outlook (1200Z Jun 25)... 20% chance of tropical cyclone formation (offshore and southeast of the Texas/Mexico border near 25N-96W)
IOH 120 Hr Outlook (1200Z Jun 26)... 20% chance of tropical cyclone formation (offshore of southeastern Texas near 27N-96.5W)
*****National Hurricane Center (hurricanes.gov) official outlook as of 10:35 AM EDT**************************
Formation chance through 48 hours... 50%
Formation chance through 7 days... 60%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).
0000Z (Jun 21) CMC Model Run...
**For area of interest #6... makes landfall at Florida/Georgia border at 24 hours... quickly dissipates inland shortly thereafter
**For area of interest #7... develops into a tropical depression offshore of northern Veracruz at 42 hours... weakens to a remnant low while then drifitng west-northwest into the Tamaulipas/Veracruz border region through 84 hours... dissipates inland shortly thereafter
**Tropical wave currently at 55W longitude crosses the Lesser Antilles and Caribbean Sea and develops into a broad tropical low east of Nicaragua at 150 hours... the tropical low makes landfall on the northeast coast of Nicaragua at 168 hours
0000Z (Jun 21) ECMWF Model Run...
**For area of interest #6... initialiazed at 0 hours as a surface trough instead of a compact tropical low... the trough makes landfall on northeast coast of Florida at 18 hours and dissipates inland shortly thereafter
**For area of interest #7... develops into a broad tropical low offshore of Veracruz at 36 hours... proceeds to drift northwest into the Veracruz and Tamaulipas coastline through 96 hours while weakening to a north-south elongated trough (the trough dissipates shortly thereafter)
0600Z (Jun 21) GFS Model Run...
**For area of interest #6... initialiazed at 0 hours as a surface trough instead of a compact tropical low... the trough makes landfall at the Florida/Georgia border at 21 hours and proceeds to dissipate inland shortly thereafter
**For area of interest #7... proceeds to develop into a tropical depression offshore of northern Veracruz thorugh 30 hours... weakens to a remnant low while then drifitng west-northwest into the Tamaulipas/Veracruz border region through 72 hours... dissipates inland shortly thereafter
0600Z (Jun 21) NAVGEM Model Run...
**For area of interest #6... makes landfall on northeast coast of Florida through 12 hours while weakening to a trough... the remnant trough dissipates inland shortly thereafter
**For area of interest #7... through 48 hours develops into an NW/SE elongated tropical low offhsore of Veracruz through 48 hours... although it later consolidates into a single center it makes landfall over northern Veracruz through 96 hours without tropical cyclone formation beforehand... dissipates inland shortly thereafter
**Due to a belt of divergence between south side of upper vorticity band across the northern Gulf of Mexico and north side of tropical upper ridge cell... a broad low pressure field persists across Bay of Campeche... western Caribbean... and adjacent regions in wake of area of interest #7 (96 to 138 hours)... the band of upper vorticity collapses through 162 hours due to prolonged isolation from high-latitude cold air which allows the supporting tropical upper ridge cell and associated outflow to expand... resulting in an eastern Bay of Campeche tropical low by 162 hours (tropical cyclone formation suggested not long after)
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