MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #159
*******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 OCTOBER 24 2020 8:38 PM EDT...
See Hurricane Epsilon and tropical depression twenty-eight sections below for the two currently active tropical cyclones in the Atlantic basin. See area of interest sections below for areas in the Atlantic being monitored for tropical cyclone formation.
Elsewhere...another tropical disturbance may emerge to the east of the Lesser Antilles...see area of interest #1 section below for more details.
HURRICANE EPSILON...While accelerating northeastward across the open northwest Atlantic over the last 24 hours...Epsilon has only slightly weakened from 85 to 80 mph maximum sustained winds. The latent heat release of Epsilon's thunderstorms since yesterday has weakened the residual upper vorticity to the west while causing it to tilt into a northwest-to-southeast axis...a configuration that has kept the westerly wind shear from the vorticity low while increasing the supportive upper divergence to the east of the axis and over the hurricane. This is likely a major contributing factor for Epsilon's minimal weakening despite the hurricane moving into waters below 26 deg C. Epsilon is being accelerated northeastward by the current eastern Canada upper trough and surface frontal cyclone. The eastern divergence zone of this upper trough will intensify the eastern Canada frontal cyclone further as it moves into the far north Atlantic...and will keep Epsilon's strength elevated as it transitions into a remnant frontal cyclone once it loses its central thunderstorms and warm core to the cooler waters. Models in agreement that the two frontal cyclones will then merge southeast of Greenland and southwest of Iceland by Monday...with the merged and intense storm likely to bring very rough seas reaching the coasts of Iceland and Greenland.
0 Hr Position (1800Z Oct 24)...80 mph maximum sustained wind hurricane centered in the northwest Atlantic at 38.5N-59W
IOH 24 Hr Forecast (1800Z Oct 25)...Non-tropical remnant frontal cyclone centered southeast of Newfoundland at 45N-50W
TROPICAL DEPRESSION TWENTY-EIGHT...After quiet a few days of watching the broad low pressure in the western Caribbean Sea...it has finally consolidated into a tropical depression centered west-southwest of the Cayman Islands. As of 1800Z...the NHC has the surface center at 18.7N-83W...but satellite imagery suggests a mid-level spiral center to the southeast near 18N-82.5W. By 24 hours a shortwave upper trough currently moving rapidly eastward over Louisiana will interact with the depression. I forecast an east lean in the north drift of the depression due to the push of the shortwave...and also in case the surface center consolidates toward the mid-level one where the thunderstorm activity is stronger. I also forecast only gradual strengthening in the short term due to the expected burst of shear to be induced by the shortwave. At 48 hours once the shortwave passes...this system will be left behind in a more favorable low shear and upper outflow environment beneath the expanding upper ridge over the western Caribbean...Gulf of Mexico...and eastern United States to be supported by warm air advection ahead of a frontal system to approach from the central and western US. Therefore by 48 and 72 hours I forecast strengthening into a strong tropical storm and then category 1 hurricane...but do not show a strength higher than category 1 as land interaction with western Cuba may be a mitigating factor. It is also during this time models continue to show a narrower surface ridge weakness tied to the incoming frontal system from the central and western US...with surface ridges on either side of the front being more intact. This will result in a more westward angle in track as this system crosses western Cuba and enters the Gulf of Mexico. Weakening is then shown after 72 hours as the upper trough of the incoming frontal system will be likely imparting increasing wind shear...but I show a slower weakening rate than previous as the 0600Z GFS model run from earlier today trended with a slightly more amplified upper trough which would make the upper flow more southerly and less westerly...a little more in alignment with the forecast track such that the shear would be less intense. The northward track is also expected to bend more eastward by 96 and 120 hours as the incoming front and upper trough take over the steering. As this system merges with the front and becomes supported by the eastern divergence zone of the upper trough...it will transition into a non-tropical remand frontal cyclone as it makes landfall along the eastern US Gulf coast. Even as it becomes less tropical...this system still has potential for high winds and coastal storm surge as it will only slowly weaken due to the support of the upper trough.
My updated forecast track is shifted west of the previous due to the current position of the depression...but not as far west as the NHC due to a possible short term drift towards the east for reasons mentioned in the prior paragraph. With these forecast adjustments...the potential for tropical storm conditions remains for the Cayman Islands thru tomorrow. Strong tropical storm conditions have become more likely for western Cuba where preparations should be underway...but hurricane force conditions are less likely as the depression has not become a tropical storm just yet. The potential for tropical storm conditions in the Florida Keys has dropped...but has increased for Quintana Roo province in the northeastern Yucatan peninsula should the depression in fact travel as far west as the global model guidance and NHC forecast show. Interests along the US Gulf coast along the Florida panhandle...Alabama and Mississippi coasts...and southeast Louisiana coast should also keep an eye on this system as it could bring high wind and coastal storm surge impact even as a vigorous non-tropical system sometime next week. I recommend gathering storm preparation supplies early to avoid a last minute rush in crowded stores amid the COVID 19 virus outbreak...and when venturing out in public during preparation wearing a mask and frequent hand sanitizing will reduce your exposure to the virus. In case you may have to relocate from impacts such as coastal storm surge...think of a hotel or family/friend residence as a public shelter may not be as ideal for controlling your exposure to the COVID 19 virus.
0 Hr Position (1800Z Oct 24)...30 mph maximum sustained wind tropical depression centered west-southwest of the Cayman Islands at 18.7N-83W
IOH 24 Hr Forecast (1800Z Oct 25)...45 mph maximum sustained wind tropical storm centered just west of Grand Cayman Island at 19.2N-81.5W
IOH 48 Hr Forecast (1800Z Oct 26)...60 mph maximum sustained wind tropical storm centered just west of the Isle of Youth of western Cuba at 21.5N-83.5W
IOH 72 Hr Forecast (1800Z Oct 27)...80 mph maximum sustained wind hurricane centered in the southern Gulf of Mexico at 24.5N-88.5W
IOH 96 Hr Forecast (1800Z Oct 28)...70 mph maximum sustained wind tropical storm centered over the northern Gulf of Mexico at 26.8N-88.5W
IOH 120 Hr Forecast (1800Z Oct 28)...45 mph maximum sustained wind frontal cyclone centered over the Alabama/Georgia border at 32.5N-85W
AREA OF INTEREST #1...The vigorous tropical wave of low pressure in the central tropical Atlantic is becoming less organized as it encounters increasing shear from western Atlantic upper vorticity getting pushed into the path of the tropical wave...and this is my final statement on this wave on this blog as tropical cyclone formation is not possible. However it should be noted that over the next few days this upper vorticity could amplify enough over the Lesser Antilles to reduce shear and increase upper divergence to the east of the Lesser Antilles...possibly setting off another tropical disturbance. This amplification would be in response to a general expansion of warm upper ridging over the Caribbean...Gulf of Mexico...eastern United States...and western Atlantic caused by southerly warm surface flow ahead of a vigorous frontal system to approach from the western and central US. The longevity of such a tropical disturbance east of the Lesser Antilles will depend on how the shortwave upper trough mentioned in area of interest #2 merges with the upper vorticity to hang out over the Lesser Antilles...with an east-west configuration of the potential merger making westerly wind shear too high and ending the disturance...or north-south configuration of the merger keeping westerly wind shear lower and allowing the disturbance to continue.
IOH 24 Hr Outlook (1800Z Oct 25)...0% chance of tropical cyclone formation (northeast coast of Venezuela near 10N-62W)
AREA OF INTEREST #2...A shortwave upper trough moving rapidly eastward across Louisiana is producing a squall of showers and thunderstorms over the southeast United States with its eastern divergence zone. As it continues into the western Atlantic...this upper trough will likely spread moisture and rainfall from tropical depression twenty-eight northeastward into south Florida and the western Bahamas...and it is likely this upper trough amplifies enough to drop wind shear levels and increase upper-level divergence for the formation of a surface low pressure near Bermuda as models have been increasingly showing. The shortwave upper trough will be amplifying in response to amplifying warm upper ridging over the eastern United States...Gulf of Mexico...and western Caribbean Sea courtesy of warm surface southerly flow to occur ahead of a substantial upper trough and surface frontal system to approach from the western and central US. However I only have low odds of development as the water temps near Bermuda are just below the 26 deg C threshold needed for development...but I do have odds as high as 20% as most models now agree on some sort of a surface low pressure forming. By 72 hours...a strengthening surface ridge to the northeast (induced by the western convergence zone of the upper trough tied to a powerful northeast Atlantic storm comprised of the the remnants of Epsilon and current east Canada frontal cyclone) should send the forecast surface low northeastward which will decouple it from the divergence zone of the fast moving shortwave upper trough...and this is when I drop odds of tropical development back to 0%
IOH 24 Hr Outlook (1800Z Oct 25)...0% chance of tropical cyclone formation (offshore of the southeastern United States near 32N-77W)
IOH 48 Hr Outlook (1800Z Oct 26)...20% chance of tropical cyclone formation (Bermuda near 32N-65W)
IOH 72 Hr Outlook (1800Z Oct 27)...0% chance of tropical cyclone formation (western Atlantic near 35N-60W)
...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 Epsilon..accelerates rapidly into the open North Atlantic and merges with another frontal cyclone by 60 hours. For tropical depression twenty-eight...shifts westward into the Yucatan peninsula by 78 hours without strengthening....makes landfall in south-central Louisiana as a remnant non-tropical frontal low by 120 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...shortwave upper trough produces a surface trough of low pressure just north of TD 28 and offshore of the southeastern United States by 48 hours...compact tropical cyclone suggested at 32N-70W at 60 hours...passes just north of Bermuda at 90 hours...dissipates into a remnant surface trough shortly thereafter.
0000Z ECMWF Model Run...For Hurricane Epsilon...accelerates rapidly into the open North Atlantic and merges with another frontal cyclone between 48 and 72 hours. For tropical depression twenty-eight...becomes a tropical storm at 19N-83W at 24 hours... strengthens while moving into the Yucatan channel between Cuba and the Yucatan peninsula at 72 hours...makes landfall in southeast Louisiana at 120 hours as a tropical cyclone transitioning into a non-tropical frontal system. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...shortwave upper trough produces a surface low pressure center at 32N-77W by 48 hours...compact tropical cyclone formation suggested at 33.5N-73.5W at 72 hours...weakens to a remnant surface trough northwest of Bermuda by 96 hours.
0600Z GFS Model Run...For Hurricane Epsilon...accelerates rapidly into the open North Atlantic and merges with another frontal cyclone by 60 hours. For tropical depression twenty-eight...moves into Yucatan channel between Cuba and Yucatan peninsula by 60 hours...makes landfall in southeast Louisiana as a remnant non-tropical frontal low by 120 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...shortwave upper trough produces a surface trough of low pressure just north of TD 28 and offshore of the southeastern United States by 48 hours...elongated surface low forms over Bermuda by 66 hours...possible compact tropical cyclone formation northeast of Bermuda at 78 hours...weakens to a surface trough at 36N-59W at 96 hours.
0600Z NAVGEM Model Run...For Hurricane Epsilon...accelerates rapidly into the open North Atlantic and merges with another frontal cyclone at 66 hours. For tropical depression twenty-eight...strengthens into a tropical storm at 19.5N-83W at 30 hours...passes in the Yucatan channel between Cuba and the Yucatan peninsula at 66 hours...makes landfall in the Florida panhandle at 102 hours as a tropical cyclone transitioning into a non-tropical frontal cyclone...remnant frontal cyclone located over Virginia at 120 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...shortwave upper trough produces a surface trough of low pressure just north of TD 28 and offshore of the southeastern United States by 48 hours...possible compact tropical cyclone formation west-northwest of Bermuda near 33N-67.5W at 60 hours...weakens to a surface trough at 35N-62W at 102 hours.