MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #79
*******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.**********
...SATURDAY AUGUST 14 2021 12:22 AM EDT...
See Fred and depression Seven sections below for an update on both tropical depressions… and possible impacts to land each could bring in the coming days.
Elsewhere...satellite imagery suggests the recent round of tropical waves emerging from Africa are being suppressed by dry Saharan air as they enter the Atlantic. None of the models forecast development from these waves at this time.
TROPICAL DEPRESSION FRED... Over the last several hours and while moving west-northwest across Cuba… Fred is back to struggling while the strongest thunderstorms became displaced southeast of center due to westerly shear from lingering upper vorticity located near the Florida west coast. This appears to also have caused Fred to regenerate south closer to the displaced thunderstorms such that the center is over Cuba instead of offshore of the north Cuban coast as was the case earlier. Due to Fred being south and west of the previous forecast… my updated one is adjusted south and west accordingly. As the current frontal low over northeast Canada departs and a surface ridge builds over the eastern US... the tail end of the front driven by the frontal low is forecast to linger as a surface ridge weakness over the interior southeast US and to the south of that surface ridge with the support of the divergence zones of the lingering upper vorticity near the west Florida coast and also upper vorticity to be cut-off from the frontal low’s upper vortex in the vicinity of the north-central US. The forecast track philosophy is to bring Fred west-northwest and then northwest while aiming for the surface ridge weakness.
Due to Fred’s struggles… I have lowered the short-term intensity forecast. A reduction in wind shear is still expected as the latest models show the lingering upper vorticity near the west Florida coast dissipating by 48+ hours. This seems plausible as Fred despite its struggles is still showing strong thunderstorm activity whose latent heat release would help weaken the cool core upper vorticity. Thus my long term intensity forecast just before landfall on the northeastern US Gulf of Mexico coast still brings Fred up to 60 mph max sustained winds… and the NHC has also reverted back to this intensity in their landfall forecast as of this writing. I do not support a higher intensity than this as the aforementioned north-Central US upper vorticity may produce light shear with some upper southwesterly flow over the forecast landfall region.
The following land areas will have to watch for arrival of tropical storm conditions (gusty winds... heavy rain with flash flood potential... and coastal sea swells) in the coming days:
** For Cuba… heavy rains and resulting flooding are the primary concerns over the central and western parts of the nation over the next several hours. The potential for gusty winds is low as Fred is currently hampered from strengthening due to disruptive westerly shear and also as the center is over Cuba instead of offshore water.
**Based on the latest Satellite pictures… heavy rain potential for the Bahamas has ended.
**Interests across south Florida and the Florida Keys should have finished preparing for possible tropical storm conditions… albeit the latest forecast is adjusted further south away from the region and is also weaker as far as winds. However as we progress into Saturday morning… the risk of heavy rains and resulting flooding will increase as moisture from Fred interacts with the divergence zone of upper vorticity located near the Florida west coast… resulting in thunderstorm potential with heavy downpours.
**Interests across the northwest Florida peninsula coast are not likely to see tropical storm conditions if the current forecast track holds… however coastal sea swells and rip currents are still possible this weekend.
**Interests across the eastern Florida panhandle and southwest Georgia are less likely to see tropical storm force winds if the latest forecast holds. However heavy rains and coastal sea swells are likely by late this weekend and into Monday.
**I recommend interests in the western Florida panhandle and southern Alabama gather storm prep supplies early as Fred is forecast to be a 60 mph max sustained wind tropical storm in the region late this weekend and into Monday.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Aug 14)… 35 mph maximum sustained wind tropical depression centered over western Cuba at 22.5N-80.2W
IOH 24 Hr Forecast (0000Z Aug 15)… 40 mph maximum sustained wind tropical storm centered offshore of northwestern Cuba at 24N-83W
IOH 48 Hr Forecast (0000Z Aug 16)… 45 mph maximum sustained wind tropical storm centered offshore of western Florida at 27N-85W
IOH 72 Hr Forecast (0000Z Aug 17)… 60 mph maximum sustained wind tropical storm centered over the northeastern Gulf of Mexico at 28.5N-87.5W
IOH 96 Hr Forecast (0000Z Aug 18)… 30 mph maximum sustained wind tropical depression centered over the southern Mississippi/Alabama border at 32N-88.5W
IOH 120 Hr Forecast (0000Z Aug 19)… remnant low centered over western Tennessee at 36N-88W
TROPICAL DEPRESSION SEVEN…The low pressure spin associated with the vigorous tropical wave of low pressure in the central Atlantic developed a more defined center to be classified as the seventh tropical depression of the 2021 Atlantic Hurricane Season. The depression continues its west-northwest march with little change as the thunderstorms remain limited on the east side of its low pressure spin due to dry Saharan air... and on the west side continue to wax and wane instead of persist. The brisk west-northwest track suggests this system is being channeled into strong east-southeasterly flow on the east side of the large tropical wave to the west that used to be tagged as invest 92-L… and the forecast track below is a continuation of the current track for the first 48 hours. By 72 and 96 hours… the forecast track is bent a little more north in response to the surface ridge weakness created by Fred in the eastern Gulf of Mexico and also the lingering tail end of a front over the interior southeast US (front to be left behind by the current eastern Canadian frontal cyclone). Note the forecast track has shifted to the west due to the faster than anticipated forward speed… and now brings this system into the northern Lesser Antilles by early Sunday.
Because the depression remains a struggling system on satellite pictures… I only forecast a peak intensity of minimal tropical storm strength (40 mph max sustained winds) for tomorrow… and then bring down the intensity to a tropical depression and then remnant low once this system moves directly into shearing winds generated by the patch of upper vorticity lingering northeast of the Bahamas. Interests in the northern Lesser Antilles… Virgin Islands… and Puerto Rico should prepare for possible gusty wind and heavy rains to arrive on Sunday. The Dominican Republic is less likely to see gusty winds on Monday as this system likely weakens from wind shear… but heavy rains are possible. I currently forecast that the rainfall risk is low for the Bahamas as this system moves below suppressing upper convergence on the west side of the upper vorticity and east side of the current west Atlantic upper ridge cell.
0 Hr Position (0000Z Aug 14)… 35 mph maximum sustained wind tropical depression centered at 15.6N-53.1W
IOH 24 Hr Forecast (0000Z Aug 15)… 40
mph maximum sustained tropical storm centered just east of the northern Lesser Antilles at 17N-59W
IOH 48 Hr Forecast (0000Z Aug 16)… 35 mph maximum sustained wind tropical depression centered over the Virgin Islands at 18N-65W
IOH 72 Hr Forecast (0000Z Aug 17)… 35 mph maximum sustains wind tropical depression centered just offshore of the north Dominican Republic north coast near 19.5N-69.5W
IOH 96 Hr Forecast (0000Z Aug 18)… Remnant low centered over the southeastern Bahamas at 21.5N-72.5W
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z CMC Model Run...
**For tropical depression Fred...loses closed circulation over the next 6 hours… re-established a closed circulation just northwest of Cuba at 30 hours… regains tropical storm status at 48 hours near 26.5N-85W… makes landfall over western Florida panhandle at 78 hours… remnant inland trough of low pressure located over Kentucky at 120 hours
**For tropical depression seven… weakens to a remnant trough at 6 hours… remnant trough/low passes over northern Lesser Antilles… Virgin Islands… and Puerto Rico thru 54 hours… remnant trough/low located over western Bahamas at 120 hours.
1200Z ECMWF Model Run...
** For tropical depression Fred... exits northwest Cuba at 24 hours… while offshore of the western Florida panhandle regains tropical storm status by 72 hours… remnant inland trough of low pressure located over eastern Tennessee at 120 hours
**For tropical depression seven… passes over northern Lesser Antilles… Virgin Islands… and Puerto Rico thru 48 hours while weakening to a remnant trough/low… remnant trough/low located over western Bahamas at 120 hours.
**Strong tropical wave forecast to emerge from Western Africa between 72 and 96 hours... center of broad low pressure spin passes over the Republic of Cabo Verde Islands at 120 hours… center of broad low pressure spin located at 16N-31W at 144 hours.
1800Z GFS Model Run...
**For tropical depression Fred... loses closed circulation over the next 3 hours… regains closed circulation offshore of western Florida at 26N-83W at 39 hours… regains tropical storm strength at 26.5N-84.5W at 48 hours… weakens to a remnant low while approaching landfall at the western Florida panhandle thru 96 hours… remnant inland trough of low pressure located over AL/GA/FL border region at 120 hours.
**For tropical depression seven… loses closed circulation over the next 3 hours… remnant trough/low passes over northern Lesser Antilles… Virgin Islands… and Puerto Rico thru 48 hours… remnant trough/low passes over Haiti and the Dominican Republic thru 84 hours… remnant trough/low located over eastern Cuba at 120 hours.
1200Z NAVGEM Model Run...
** For tropical depression Fred... regains tropical storm status on northwest coast of Cuba at 18 hours… passes over the western Florida Keys at 30 hours… gains hurricane strength at 54 hours near 27.7N-85.5W… at 72 hours makes landfall over the western Florida panhandle… remnant low located over West Virginia at 120 hours.
**For tropical depression seven… initialized as a surface trough… trough passes over the northern Lesser Antilles… Virgin Islands… and Puerto Rico thru 60 hours… trough located over the central Bahamas at 120 hours.
**Strong tropical wave forecast to emerge from Western Africa at 60 hours... passes over the southern Republic of Cabo Verde Islands at 120 hours.