MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #144
*******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.**********
...FRIDAY OCTOBER 9 2020 1:25 PM EDT...
See Major Hurricane Delta section below for the only currently active tropical cyclone in the Atlantic basin. See area of interest sections below for other areas being monitored for tropical development.
Elsewhere...a shortwave upper trough over western Canada and its associated front over the northern United States will quickly be guided southeastward into the open central Atlantic by the southwest sides of the current eastern Canada frontal cyclone and its vigorous upper trough. Models differ on whether or not the shortwave upper trough will amplify into a cut-off upper vortex whose eastern divergence zone triggers an open central Atlantic surface cyclone along the front in about 4 to 5 days...with the surface cyclone potentially acuqiring thunderstorms and tropical characteristics over warm enough waters and the instability of the cold temps of the upper vortex. Whether or not this event happens hinges upon how strong the warm western Atlantic upper ridge will be in the warm sector of a strong frontal cyclone to develop over western North America...with a stronger more amplified upper ridge causing the shortwave upper trough's amplification into a possible cut-off upper vortex. The CMC leads in showing possible subtropical cyclone formation in the open central Atlantic in this morning's model guidance. Waiting for more of a model consensus before deciding to add an area of interest for subtropical development.
MAJOR HURRICANE DELTA...Rainfall spreading across southeastern Texas and western half of Louisiana...conditions to detereorate further along the south-central Lousiana...southwestern Louisiana...and southeastern Texas coasts as coastal storm surge and wind will increase throughout the day...with damaging hurricane force winds now imminent by tonight and over southwestern Louisiana in the same areas badly damaged by Hurricane Laura in late August as the track of Delta has stayed further to the west overnight. The inland potential for gusty tropical storm force winds with some damage potential by tomorrow morning has likewise shifted westward to incude western Mississippi and southeastern Arkansas. In the last 24 hours Delta's new eye has allowed it to intensify to a category 3 with 120 mph maximum sustained winds...but overnight this eye has lost its definition in satellite pictures and by 5 AM EDT (4 AM CDT) the National Hurricane Center was reporting the eye was slightly tilting northeastward with height as the upper trough over the Texas/Mexico region that has been turning Hurricane Delta northward has begun to lightly shear the hurricane. As of the most recent 11 AM EDT advisory Delta has just begun to weaken to 115 mph maximum sustained winds...and in my estimation will come ashore as a high-end category 2 with 105 to 110 mph maximum sustained winds while crossing over cooler northern Gulf of Mexico water and as the increasing shear begins to negatively affect the hurricane. I have nudged the intensity forecast upward a bit as Delta is above my previous intensity forecast. The more westward position of Delta is probably due to a delay in the arrival of the southwesterly upper flow from the east side of the aforementioned upper trough...as evidenced by the thunderstorm clouds still being largely symmetric about the center of the hurricane as opposed to be being biased towards the northeast half...and perhaps the latent heat release of Delta's tremendous thunderstorm clouds has been able to keep what is a relatively weak cold core upper trough more at bay. However the increase in southwesterly upper flow and resulting northeastward turn of Delta is still imminent as a shortwave upper trough moving quickly across western Canada (which is driving a surface frontal system across the northern United States) will push the upper trough over Texas/Mexico eastward into Delta. The westward-adjusted forecast track takes the northeastward turn of Delta across southwestern Louisiana and just east of the Texas border for landfall...and into western Kentucky instead of eastern Kentucky by Sunday. The forecast track inland is largely based on Delta following the eastern divergence zone of the incoming Texas/Mexico upper trough as the upper trough moves east...as Delta transitions into a gradually weakening remnant frontal low pressure supported by the upper trough's divergence. See home page bulletins for more on the expected impacts from Hurricane Delta.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Oct 9)...120 mph maximum sustained wind major hurricane centered over the northwestern Gulf of Mexico at 27.5N-93.8W
IOH 24 Hr Forecacst (1200Z Oct 10)...50 mph maximum sustained wind tropical storm transitioning to a remnant frontal cyclone centered over the Mississippi/Arkansas border at 33.5N-90.8W
IOH 48 Hr Forecast (1200Z Oct 11)...Remnant frontal low pressure centered over western Kentucky at 37.5N-86W
AREA OF INTEREST #1...Thunderstorm activity in the north-central Caribbean Sea has reduced and remain disorganized...and has moved on to the western Caribbean Sea in an apparent divergence zone on the south side of the upper vortex that has been retorgrading westward through the region. The National Hurricane Center TAFB surface analysis has added a surface trough in the central Caribbean Sea being treated as a tropical wave of low pressure...perhaps then it is possible the divergence zone of the upper vortex has triggered a surface trough of low pressure before moving on to the western Caribbean Sea...therefore for continuity I am tying this area of interest to the north side of the new tropical wave as opposed to the upper vortex now located further to the west. Upper-level winds will become more conducive for this tropical wave to potentially develop as the cold core upper vortex disspiates while remaining cut-off from higher latitude cold air...with the sprawling western Atlantic to Gulf of Mexico upper ridge with its low shear and upper outflow dominating the region. But given a lack of computer model support actutally showing development I retain very low 5% odds of tropical cyclone formation for the next 5 days. Forecast track in the outlook below shows a west-northwest track around the southwest side of the current surface ridge over the eastern United States...followed by a slow down in forward speed once the tropical wave reaches the southern Gulf of Mexico due to the ridge weakness to be created by the remnant frontal low of Delta and vigorous frontal cyclone to develop over western North America behind Delta with the support of an amplified upper trough incoming into the western US. Models continue to trend with a more amplified upper trough and resulting stronger frontal cyclone such that stronger warm southerly flow ahead of the stronger cyclone washes out the cold upper trough tied to Delta's remnant...thus Delta's remnant should dissipate sooner. This...combined with the more southern position of the new tropical wave causes me to shift my forecast track away from south Florida as it will be less likely that any disturbance that develops from this wave would get caught into the surface ridge weakness tied to Delta. Instead my updated track now accelerates the tropical wave southwestward into the southwest Gulf of Mexico by 120 hours as a surface ridge builds over the southern United States in the western convergence zone of the frontal cyclone's upper trough.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 10)...0% chance of tropical cyclone formation (southwest of Jamaica and south of the Cayman Islands near 18N-80W)
IOH 48 Hr Outlook (1200Z Oct 11)...0% chance of tropical cyclone formation (western Cuba near 20N-85W)
IOH 72 Hr Outlook (1200Z Oct 12)...5% chance of tropical cyclone formation (south-central Gulf of Mexico near 22.5N-88W)
IOH 96 Hr Outlook (1200Z Oct 13)...5% chance of tropical cyclone formation (south-central Gulf of Mexico near 23N-91W)
IOH 120 Hr Outlook (1200Z Oct 14)...5% chance of tropical cyclone formation (southwestern Gulf of Mexico near 21N-95W)
AREA OF INTEREST #2...The vigorous tropical wave of low pressure in the eastern tropical Atlantic apperas to have driven a surge of dry saharan air from western Africa into the east-central Atlantic...and perhaps the dry air has caused the thunderstorm complex that was on the east side of the wave axis to fizzle out. Instead this morning renewed thunderstorm bands further to the southwest suggest an area of weak rotation near 8.5N-31W...therefore my updated outlook forecast points below are shifted southwestward while initializing the lowest pressure to be along the NHC TAFB's analyzed position of the wave axis instead of to the east of the axis. Atmospheric conditions in the short-term are favorable for additional development of this tropical wave thanks to low shear and upper outflow induced by the eastern tropical Atlantic upper ridge...but I have lowered my peak 5-day odds of tropical cyclone formation to 25% due to the current weakness in the thunderstorm intensity which suggests the dry sahran air to the northeast may be negatively affecting the tropical wave. This is still slightly higher than the NHC outlook...which has introduced this tropical wave into their outlook since yesterday afternoon...because I am giving some weight to the organized curvature of the current bands of shower and thunderstorm activity. By 72 to 96 hours...the current eastern Canada frontal cyclone and its upper trough will swing the current western Canada shortwave upper trough and its surface frontal zone (currently over the northern US) southeastawrd into the open central Atlantic...therefore the long term forecast track indicates a northward bend induced by the surface ridge weakness tied to this frontal zone. A northward bend in track is also possible by that time should this system indeed develop and become tall enough to be steered by upper southwesterly flow associated with the frontal zone's shortwave upper trough. Odds of development are lowered from the peak of 25% by days 4 and 5 as this upper southwesterly flow is expected to negatively shear this tropical wave.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Oct 10)...0% chance of tropical cyclone formation (eastern tropical Atlantic near 9.5N-36W)
IOH 48 Hr Outlook (1200Z Oct 11)...10% chance of tropical cyclone formation (central tropical Atlantic near 9.9N-41W)
IOH 72 Hr Outlook (1200Z Oct 12)...25% chance of tropical cyclone formation (central tropical Atlantic near 11.5N-46W)
IOH 96 Hr Outlook (1200Z Oct 13)...10% chance of tropical cyclone formation (central tropical Atlantic near 13N-50W)
IOH 120 Hr Outlook (1200Z Oct 14)...0% chance of tropical cyclone formation (central tropical Atlantic near 15N-54W)
...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 Major Hurricane Delta...after making landfall remnant low pressure loses identity over the Mississippi/Tennessee border and ahead of incoming western US cold front by 72 hours. For areas of interest #1 and #2...no tropical cyclone formation shown. Elsewhere...current frontal zone moving quickly across the northern United States moves into the open central Atlantic by 96 hours...surface cyclone quickly develops along the front near 33N-53.5W under the support of an upper trough fragment amplifying into a cold-core upper vortex at 120 hours...potential for surface cyclone to acquire tropical characteristics suggested after 120 hours.
0000Z ECMWF Model Run.....For Major Hurricane Delta...after making landfall remnant low pressure loses identity over the Tennessee/Kentucky border and ahead of incoming western US cold front just after 72 hours. For areas of interest #1...no tropical cyclone formation shown. For area of interest #2...tropical wave organizes into a tropical low east of the Lesser Antilles near 14.5N-56W. Elsewhere...current frontal zone moving quickly across the northern United States moves into the open central Atlantic by 96 hours...broad surface low develops along the front near 34.5N-46W by 168 hours.
0600Z GFS Model Run...For Major Hurricane Delta...after making landfall remnant low pressure loses identity over western Tennessee and ahead of incoming western US cold front at 66 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...tropical wave organizes into a tropical low pressure at 10N-46W at 66 hours...tropical low weakens to a tropical wave near 55W at 102 hours. Elsewhere...tropical wave with organized low pressure spin emerges from western Africa at 102 hours...possible development as tropical wave moves across eastern tropical Atlantic suggested in the long range.
0600Z NAVGEM Model Run...For Major Hurricane Delta...after making landfall remnant low pressure loses identity over western Kentucky and ahead of incoming western US cold front at 78 hours. For areas of interest #1 and #2...no tropical cyclone formation shown.