MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #142
Updated: Oct 8
*******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 OCTOBER 7 2020 12:15 PM EDT...
See Hurricane Delta section below for the only currently active tropical cyclone in the Atlantic basin. See area of interest section below concerning the current area of disturbed weather in the northeastern Caribbean Sea.
HURRICANE DELTA...Last evening while approaching the northeastern Yucatan peninsula...the definition of Hurricane Delta's eye on colorized infrared satellite disappeared and the hurricane weakened to a high-end category 2 hurricane with 110 mph maximum sustained winds for its landfall this morning. Perhaps then an eye wall replacement cycle caused the weakening...but interests in the northeastern Yucatan need to remain hunkered down until the high damaging winds and coastal storm surge of Hurricane Delta clears the region. The hurricane has tracked slightly north of my previous forecast track and therefore its inner core received less land exposure...and the hurricane does not appear to have grown much in size while absorbing the remnant low pressure of Gamma. Therefore the hurricane remains a relative smaller storm that can undergo rapid intensity fluctuations...therefore along with my northward adjustment in the forecast track I have increased the intensity forecast to show Delta regaining category 3 status as it moves into the open western Gulf of Mexico (for now not forecasting an intensity higher than this as I speculate Delta will need some time to re-establish an eye after last night's eye wall replacement cycle coupled with this morning's landfall). The track into the western Gulf of Mexico will be due to the central United States surface ridge which will recover in the next 24 hours under the western convergence zone of the latest upper trough moving into eastern North America.
After 24 hours...Delta will interact with the current upper trough fragment over Mexico which will swing eastward toward Delta...and so shear induced by the upper trough by 48 hours is why I forecast Delta to weaken back to a category 2 as it approaches the United States Gulf coast. With my northward adjusted track forecast in the short-term...this will cause Delta to engage with the upper trough at a location a little further north such that the upper steering flow will be a little more southerly and a little less westerly...keeping the hurricane's track less east and more northward in the longer range. Thus my updated forecast track points for the long range are nudged northwestward...shifting my forecast landfall position for late Friday to be further west over south-central Louisiana. This now increases the damaging wind threat further for south-central Louisiana...and unfortunately for southwestern Louisiana as well which got hit hard by Hurricane Laura in late August. However on the current forecast track outlined below...winds over southwestern Louisiana will be in the less severe tropical storm force zone on the west side of the hurricane...but keep in mind that if the track shifts further west then southwestern Louisiana could be in play for hurricane force winds as well. The threat of hurricane force winds has reduced for southeastern Louisiana...but tropical storm force winds remain a possibility from the east side of the hurricane. The wind threat for southern Alabama and western Florida panhandle has also greatly reduced on the latest forecast track...but coastal storm surge flooding and sea swells driven by the onshore push of wind on the east side of Delta are still expected from south-central Louisiana to the western Florida panhandle. Despite seeing increasd wind shear and lower water temperatures in the northern Gulf of Mexico...Delta will likely be a gradually weakening storm hanging on to category 2 strength at landfall time due to supportive divergence on the east side of the incoming upper trough...and therefore will likely hang on to tropical storm force for some time as it moves inland...spreading gusty winds with damage potential inland into southern and central Mississippi by early Saturday. I expect by 96 hours Delta will transition into a remnant frontal low pressure supported by the upper trough while moving well inland over the eastern United States. Heavy rainfall with flash flooding potential from Delta and its eventual remnant frontal low is a possibility across Louisiana...Mississippi...southeastern Arkansas...northwestern Alabama...Tennessee...and Kentucky.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Oct 7)...105 mph maximum sustained wind hurricane centered over the northeastern Yucatan peninsula at 21.1N-87.4W
IOH 24 Hr Forecast (1200Z Oct 8)...120 mph maximum sustained wind major hurricane centered over the western Gulf of Mexico at 23.5N-92.5W
IOH 48 Hr Forecast (1200Z Oct 9)...110 mph maximum sustained wind hurricane centered over the northwestern Gulf of Mexico at 27N-93.5W
IOH 72 Hr Forecacst (1200Z Oct 10)...50 mph maximum sustained wind tropical storm transitioning to a remnant frontal cyclone centered over central Mississippi at 32.5N-89.5W
IOH 96 Hr Forecast (1200Z Oct 11)...Remnant frontal low pressure centered over southeastern Kentucky at 37.5N-83.5W
AREA OF INTEREST #1...The tropical wave of low pressure in the open central Atlantic to the east of the Lesser Antilles islands has become less defined...and according to the National Hurricane Center TAFB surface analysis has been stalled over the last 24 hours. Meanwhile in the northeastern Caribbean Sea...a cluster of thunderstorm acitivity persists under the divergence zone of an upper vortex retrograding southwestward and breaking away from the main branch of central Atlantic upper vorticity. As a result...I have shifted the area of interest west-northwestward toward the upper vortex and away from the tropical wave...with the assumption that maybe a surface low pressure develops in the current thunderstorm activity. With this cold core upper vortex expected to continuously retrograde westward aroud the sprawling west Atlantic upper ridge thru 72 hours...and dissipate by 96 hours while remaining cut-off from higher latitude cold air...the upper wind pattern will increasingly become more conducive to tropical development for any surface low pressure that does develop...as the western Atlantic upper ridge with its low shear and upper outflow overspreads the area in the wake of the upper vortex. I have lowered peak 5-day odds of tropical cyclone formation to 15% as this disturbance will have to develop its own surface low pressure as the aforementioned tropical wave of low pressure is apparently no longer a part of the disturbance. Forecast track in the outlook below is initially based on following the eastern diveregnce zone of the cut-off upper vortex in the 0600Z run of the GFS model...followed by a northward and northeastward bend in track toward the surface ridge weakness to be created by what will be the remnant frontal low pressure of Delta over the eastern United States. I drop odds of development back down to 5% by 120 hours as the forecast track outlined below takes this disturbance into shearing upper westerly winds to be induced by the upper trough to be tied to the remnant low of Delta.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 8)...0% chance of tropical cyclone formation (south of Haiti near 16.5N-73.5W)
IOH 48 Hr Outlook (1200Z Oct 9)...5% chance of tropical cyclone formation (just southeast of Jamaica near 17.5N-76W)
IOH 72 Hr Outlook (1200Z Oct 10)...10% chance of tropical cyclone formation (just south of Grand Cayman Island near 19N-81W)
IOH 96 Hr Outlook (1200Z Oct 11)...15% chance of tropical cyclone formation (western Cuba near 22.5N-84W)
IOH 120 Hr Outlook (1200Z Oct 12)...5% chance of tropical cyclone formation (south Florida near 25.5N-81W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
0000Z CMC Model Run... For Hurricane Delta...makes landfall over the Texas/Louisiana border at 72 hours...located over the Indiana/Illinois border at 120 hours as a remnant low pressure. For area of interest #1...no tropical cyclone formation shown.
0000Z ECMWF Model Run.....For Hurricane Delta...makes landfall over the Texas/Louisiana border at 72 hours...located over the Missouri/Arkansas/Tennesee/Kentucky border region at 120 hours as a remnant low pressure. For area of interest #1...no tropical cyclone formation shown.
0600Z GFS Model Run...For Hurricane Delta...makes landfall over southwestern Louisiana at 60 hours...located over the eastern United States as a broad remnant low pressure at 120 hours. For area of interest #1...no tropical cyclone formation shown. Elsewhere...a tropical wave with low pressure spin emerges from western Africa by 126 hours with weak tropical cyclone formation suggested south of the Republic of Cabo Verde Islands by 168 hours.
0600Z NAVGEM Model Run...For Hurricane Delta...makes landfall over south-central Louisiana at 66 hours...located over Ohio at 120 hours as a remnant frontal cyclone...no tropical cyclone formation shown. For area of interest #1...no tropical cyclone formation shown. Elsewhere...tropical wave of low pressure currently emerging from western Africa organizes into tropical low pressure east of the southern Lesser Antilles at 138 hours...low pressure moves slowly northwestward and organizes into a tropical cyclone just east of the central Lesser Antilles at 168 hours.