MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #160
*******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.**********
...SUNDAY OCTOBER 25 2020 6:08 PM EDT...
See Hurricane Epsilon and Tropical Storm Zeta sections below for the two currently active tropical cyclones in the Atlantic basin. See area of interest section below for surface trough of low pressure offshore of the southeastern United States being monitored for development.
Elsewhere...upper vorticity over the Lesser Antilles could amplify enough 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 #1 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.
HURRICANE EPSILON (RECENTLY DOWNGRADED TO TROPICAL STORM EPSILON)...While accelerating northeastward across the open northwest Atlantic cooler waters over the last 24 hours...Epsilon has only slightly weakened from 80 to 75 mph maximum sustained winds. Epsilon is being accelerated northeastward by the current eastern Canada upper trough and surface frontal cyclone that has recently entered the North Atlantic from the east Canada coast...and it is the eastern divergence zone of this upper trough that has kept the strength of Epsilon elevated. Once Epsilon loses its central thunderstorms and warm core soon...it will transition to a remnant frontal cyclone. Models in agreement that the two frontal cyclones (Epsilon and the one offshore of eastern Canada) will merge southeast of Greenland and southwest of Iceland in the next 24 hours...with the merged and intense storm likely to bring very rough seas reaching the coasts of Iceland and Greenland.
Update as of 5 PM EDT: Epsilon is no longer a minimal hurricane...but now a strong tropical storm with 70 mph maximum sustained winds.
0 Hr Position (1800Z Oct 25)...75 mph maximum sustained wind hurricane centered southeast of Newfoundland at 44.3N-49.4W
IOH 24 Hr Forecast (1800Z Oct 26)...Non-tropical frontal cyclone merging with second cyclone to the northwest while located at 55N-27W
TROPICAL STORM ZETA...Over the last 24 hours...the heaviest thunderstorm activity of tropical depression twenty-eight has shifted to the southern semicircle of the circulation...perhaps as the shortwave upper trough passing to the north has constricted the northern upper level outflow of the circulation. The depression has also strengthened into Tropical Storm Zeta while the surface and mid-level centers have reformed southwestward toward the stronger thunderstorm activity. I remember being stunned during the 2005 season when we reached all the way to the name Zeta in the Greek alphabet list of names...I never thought I would see such an event again in my lifetime. But the 2020 Atlantic Hurricane Season has been truly more stunning with the number of storms...and it wouldn’t surprise me at this point if we break the record set in 2005 for the most number of Atlantic tropical storms over the next month or so.
The forecast track has been adjusted southwest in the short term to account for Zeta’s center reformation mentioned in the last paragraph. Models continue to show a narrow 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...thus Zeta will begin a northwest track toward the front thanks to the ridging instead of a straight north track ahead of the front. And with the adjustment in the forecast track...this now takes Zeta into the northeast corner of the Yucatan Peninsula by 36 hours. It is also during this time the shortwave upper trough to the north passes...and Zeta 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 the frontal system to approach from the central and western US. Even though Zeta has not strengthened much so far...I have increased the short term intensity forecast due to the current intensity of the thunderstorms on the south side of Zeta...which I anticipate will quickly wrap into all quadrants of the circulation under the improving upper winds and cause Zeta to strengthen appreciably. But I do not show a strength higher than a high end category 1 as land interaction with Yucatan may be a mitigating factor. Weakening is shown after 48 hours as the upper trough of the incoming frontal system will be likely imparting increasing wind shear...and despite the initially higher intensity forecast I keep the longer term intensity forecast the same as the 1200Z GFS model run shows with a slightly more north location of the upper trough which would make the upper flow more westerly and less southerly...a little less in alignment with the forecast track such that the shear would be stronger. The northward track is also expected to bend more eastward by 72 and 96 hours as the incoming front and upper trough take over the steering...and I have shown a faster northeast track in accordance with many of the latest model runs. As Zeta 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 will have potential for high winds and coastal storm surge as it will only slowly weaken due to the support of the upper trough.
With these forecast updates...the potential for tropical storm conditions has disappeared for the Cayman Islands. Strong tropical storm conditions remain possible for western Cuba where preparations should be underway...but hurricane force conditions are not expected as the storm track continues shifting away from the area. The potential for strong tropical storm and possible hurricane conditions has significantly increased for Quintana Roo province in the northeastern Yucatan peninsula where preparations should be underway in earnest. Interests along the US Gulf coast along the Florida panhandle...Alabama and Mississippi coasts...and southeast Louisiana coast should also keep an eye on Zeta as it will likely bring high wind and coastal storm surge impact even as a vigorous non-tropical system
sometime next week. Gusty winds could spread inland across southern Mississippi...eastern Alabama...and much of Georgia. 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.
Update as of 5 PM EDT: Zeta has strengthened to 50 mph maximum sustained winds...the chances for hurricane force conditions in Quintana Roo by 36 hours is increasing further.
0 Hr Position (1800Z Oct 25)...40 mph maximum sustained wind tropical storm centered in the western Caribbean Sea at 18N-84W
IOH 24 Hr Forecast (1800Z Oct 26)...65 mph maximum sustained wind tropical storm centered in the northwestern Caribbean Sea at 19.5N-85.5W
IOH 48 Hr Forecast (1800Z Oct 27)...90 mph maximum sustained wind hurricane centered in the southern Gulf of Mexico at 22.5N-90W
IOH 72 Hr Forecast (1800Z Oct 28)...70 mph maximum sustained wind tropical storm centered over the northern Gulf of Mexico at 27N-90W
IOH 96 Hr Forecast (1800Z Oct 28)...40 mph maximum sustained wind frontal cyclone centered over northern Georgia at 33.8N-84W
AREA OF INTEREST #1...A shortwave upper trough moving rapidly eastward toward the southeastern United States coast is producing a developing surface trough of low pressure and widespread area of showers and thunderstorms offshore with its eastern divergence zone. 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 or west of Bermuda as models have continued to show. 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 in the region are just below the 26 deg C threshold needed for development...but I do have odds as high as 20% as most models continue to agree on some sort of a surface low pressure forming. By 48 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 frontal cyclone offshore of eastern Canada) 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 to 0%. However it should be noted that some models such as the ECMWF show the surface low forming and thriving at a location further west underneath the expanding eastern United States...Gulf of Mexico...and western Caribbean Sea upper ridge...perhaps the west end of the aforementioned new surface trough offshore of the United States interacting with the upper ridge. Thus my updated forecast track is nudged westward...and my outlook may have to be adjusted further to the west and extended for a longer period of time if indeed development tries to occur in the wake of the shortwave upper trough.
IOH 24 Hr Outlook (1800Z Oct 26)...20% chance of tropical cyclone formation (west of Bermuda near 32N-67W)
IOH 48 Hr Outlook (1800Z Oct 27)...0% chance of tropical cyclone formation (western Atlantic near 35N-62W)
...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 36 hours. For Tropical Storm Zeta...moves into the Yucatan channel between Cuba and the Yucatan peninsula by 48 hours...makes landfall in southeast Louisiana at 90 hours...becomes an elongated frontal low over Tennessee by 108 hours that loses identity along front shortly thereafter. For area of interest #1...compact tropical cyclone formation suggested at 33N-69W at 42 hours...passes just north of Bermuda by 66 hours while weakening into a remnant surface trough.
0000Z ECMWF Model Run...For Hurricane Epsilon...accelerates rapidly into the open North Atlantic and merges with another frontal cyclone between 24 and 48 hours. For Tropical Storm Zeta...strengthens while moving into the Yucatan channel between Cuba and the Yucatan peninsula at 48 hours...makes landfall in southeast Louisiana at 96 hours as a tropical cyclone transitioning into a non-tropical frontal system. For area of interest #1...compact and strong tropical cyclone formation suggested at 35N-68W at 48 hours...weakens to a remnant surface trough north of Bermuda by 72 hours.
1200Z GFS Model Run...For Hurricane Epsilon...accelerates rapidly into the open North Atlantic and merges with another frontal cyclone by 24 hours. For Tropical Storm Zeta...briskly intensified into a strong hurricane by 42 hours while moving into the Yucatan channel between Cuba and the Yucatan peninsula...makes landfall as a hurricane at the Mississippi/Alabama border at 78 hours...through 102 hours passes over Georgia...western Carolinas...and Virginia as a weakening remnant frontal low...remnant frontal low emerges over the open northwest Atlantic by 120 hours. For area of interest #1...elongated surface low forms west of Bermuda by 30 hours...weakens to a surface trough northeast of Bermuda by 60 hours.
0600Z NAVGEM Model Run...For Hurricane Epsilon...accelerates rapidly into the open North Atlantic and merges with another frontal cyclone at 30 hours. For Tropical Storm Zeta...continuously strengthens till landfall in the northeastern Yucatan peninsula at 48 hours...additional strengthening into a strong hurricane till landfall in southeast Louisiana at 96 hours...remnant low located over the northern Alabama/Georgia border at 120 hours. For area of interest #1...weak surface low forms offshore of southeast Florida in 6 hours...weakens to a surface trough well north of Bermuda by 54 hours without tropical cyclone formation.