BIRDSEYE VIEW POSTS

Since 2012 on the Weather Underground (www.wunderground.com) blogs, I have been posting annotated "birdseye view" charts of the Atlantic basin, with a detailed explanation and forecasting that references the chart. From there you may know me as "NCHurricane2009." While I now do these "birdseye view" posts here, I will continue to do comments via Disqus on Weather Underground at www.wunderground.com/cat6. You can see my Disqus feed at this link for my latest comments. Feel free to reply to me with your disqus account or e-mail at IOHurricanes@outlook.com 

 
 
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MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #158

*******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 23 2020 11:46 AM EDT...

See Hurricane Epsilon section below for the only active tropical cyclone in the Atlantic basin. See area of interest sections below for areas in the Atlantic being monitored for tropical cyclone formation.


Elsewhere...A shortwave upper trough to pass north of the western Caribbean disturbance mentioned in area of interest #1 may trigger another subtropical or tropical disturbance to the west of Bermuda in the coming days...see area of interest #1 section below for more details. In addition...another similar type of disturbance supported by upper vorticity may emerge east of the Lesser Antilles...see area of interest #2 section below for more details.


HURRICANE EPSILON...While passing east of Bermuda over the last 24 hours...Epsilon has only slightly weakened from 90 to 85 mph maximum sustained winds. The latent heat release of Epsilon's thunderstorms 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. Due to the current position of Epsilon...my short-term track forecast is nudged eastward. The impending northeastward turn out to sea will be delayed for 24 more hours due to the passage of the current surface ridge over eastern Canada. Once this surface ridge shifts eastward...Epsilon after 24 hours will then be carried rapidly northeastward by the current central North America upper trough and surface frontal low currently developing over the Great Lakes region. The eastern divergence zone of this upper trough will intensify the Great Lakes frontal low into a cyclone as it moves into the far north Atlantic...and will keep Epsilon's strength elevated as it moves into waters below 26 deg C and transitions into a remnant frontal cyclone once it loses its thunderstorms and warm core to the cooler waters. Models are in general agreement that the two frontal cyclones will 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.

******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********

0 Hr Position (1200Z Oct 23)...85 mph maximum sustained wind hurricane centered northeast of Bermuda at 33.8N-61.6W

IOH 24 Hr Forecast (1200Z Oct 24)...85 mph maximum sustained wind hurricane centered in the northwest Atlantic at 36.5N-61.6W

IOH 48 Hr Forecast (1200Z Oct 25)...Non-tropical remnant frontal cyclone centered south-southeast of Newfoundland at 43N-55W


AREA OF INTEREST #1...Showers and thunderstorms continue to become better organized on the east side of the large and broad surface low pressure field in the western Caribbean Sea...at a location toward the Cayman Islands...Jamaica...and Cuba. Based on the organization shown in the lastest satellite imagery...I estimate that the lowest pressure of the disturbance is now just south of the Cayman Islands near 18N-81W...pivoting slowly northward around the remainder of the broad low pressure field off to the west. Based on the continuous organization of the disturbance...I have sharply increased short-term odds of tropical cyclone formation to 70% for the next 24 hours.


By 48 hours a shortwave upper trough currently moving rapidly eastward over Texas will interact with this disturbance. Considering that the disturbance is already consolidating before the arrival of the trough...it is unlikely for the disturbance to now relocate northeastward into the open western Atlantic waters under the divergence zone of the shortwave upper trough. However this upper trough will likely spread moisture and rainfall from this disturbance northeastward into south Florida and the western Bahamas...and it is possible the shortwave amplifies enough in the western Atlantic to drop wind shear levels and increase upper-level divergence for the formation of another subtropical or tropical disturbance to the west of Bermuda. The shortwave 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. Will handle the scenario of another possible subtropical or tropical disturbance to the west of Bermuda as another area of interest section in future updates if observations and additional computer model runs warrant. In the meantime for this disturbance...I dip odds of development downward to 60% as the passing shortwave upper trough will induce a burst of disrupting westerly shear.


Once the shortwave upper trough passes by 72 hours...this disturbance 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 mentioned in the previous paragraph. Therefore by 72 and 96 hours I raise odds of tropical cyclone formation back upward to a high 75% chance. It is also during this time models have trended with 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 toward the Gulf of Mexico during this time instead of a pure northward drift. Odds of development are dropped downward to 50% by 120 hours as the upper trough of the incoming frontal system will be likely imparting increasing wind shear...and the incoming front itself has potential to absorb this disturbance and make it less tropical in nature by that time. However even if this system loses tropical characteristics...there is longer term potential (just after 5 days) for this system to come ashore anywhere from southeast Louisiana to the Florida panhandle as a vigorous frontal cyclone supported by the eastern divergence zone of the upper trough.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1200Z Oct 24)...70% chance of tropical cyclone formation (over the Cayman Islands near 19N-81W)

IOH 48 Hr Outlook (1200Z Oct 25)...60% chance of tropical cyclone formation (between the Cayman Islands and western Cuba near 20.5N-81W)

IOH 72 Hr Outlook (1200Z Oct 26)...75% chance of tropical cyclone formation (Isle of Youth of western Cuba near 21.5N-83.5W)

IOH 96 Hr Outlook (1200Z Oct 27)...75% chance of tropical cyclone formation (southeastern Gulf of Mexico near 24.5N-85W)

IOH 120 Hr Outlook (1200Z Oct 28)...50% chance of tropical cyclone formation (northeastern Gulf of Mexico near 26.2N-87.5W)


AREA OF INTEREST #2...The vigorous tropical wave of low pressure in the central tropical Atlantic continues moving briskly westward under the influence of the strong surface ridge to the north...and within its thunderstorm activity there appears to be a weak spin on satellite animation that passed 8N-48W as of 1200Z earlier today. Over the next 24 hours upper-level winds over the tropical wave may become a little more conducive for some development as an expanding area of upper outflow potentially develops in the wake of the weakening western Atlantic cut-off upper vorticity (this weakening is expected as the cold core upper vorticity remains cut-off from high latitude colder air). However given that the tropical wave has not become better organized since yesterday...I have lowered odds of tropical cyclone formation to a very low 5%. By 48 hours...the upper vorticity is forecast to be pushed southward toward the tropical wave as the warm western Caribbean upper ridge expands from the thunderstorm latent heat release tied to the disturbance in area of interest #1...thus I drop odds of development to 0% by that time. The forecast position of the upper vorticity by that time should shield the southern Lesser Antilles and northeast coast of Venezuela from any heavy weather tied to this tropical wave by pushing the thunderstorms to the east of the wave axis...thus I do not mention these land areas in relation to this wave on the home page bulletins of this site. However it should be noted that over the next few days this upper vorticity 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...and possibly from latent heat release of thunderstorms to be induced by the divergence zone of the shortwave upper trough to roam the western Atlantic discussed in area of interest #1. The longevity of such a tropical disturbance east of the Lesser Antilles will depend on how the western Atlantic shortwave upper trough 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.

******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********

IOH 24 Hr Outlook (1200Z Oct 24)...5% chance of tropical cyclone formation (central tropical Atlantic near 9N-56W)

IOH 48 Hr Outlook (1200Z Oct 25)...0% chance of tropical cyclone formation (northeast coast of Venezuela near 10N-61W)


...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 78 hours. For area of interest #1...broad low pressure consolidates at 20N-85W at 48 hours....consolidated circulation shifts westward into the Yucatan peninsula by 90 hours without tropical cyclone formation. For area of interest #2...organizes into a low pressure spin at 9.5N-49W at 12 hours...weakens back to a tropical wave near 60W longitude by 48 hours.


0000Z ECMWF Model Run...For Hurricane Epsilon...accelerates rapidly into the open North Atlantic and merges with another frontal cyclone between 72 and 96 hours. For area of interest #1...broad low pressure consolidates just west of the Cayman Islands at 24 hours...consolidated circulation shifts westward into the Yucatan peninsula by 96 hours without tropical cyclone formation. For area of interest #2...no tropical cyclone formation shown.


0600Z GFS Model Run... For Hurricane Epsilon...accelerates rapidly into the open North Atlantic and merges with another frontal cyclone by 78 hours. For area of interest #1...broad low pressure consolidates at 20N-85W at 18 hours...consolidated circulation shifts westward into the Yucatan peninsula by 90 hours without tropical cyclone formation. For area of interest #2...no tropical cyclone formation shown. Elsewhere...shortwave upper trough produces a surface trough of low pressure just north of area of interest #1 and offshore of the southeastern United States by 66 hours...compact tropical cyclone suggested just west of Bermuda at 84 hours...weakens to a remnant low just north of Bermuda at 102 hours...remnant low weakens to a dissipating surface trough near 36N-60W by 120 hours.


0600Z NAVGEM Model Run...For Hurricane Epsilon...accelerates rapidly into the open North Atlantic and absorbs frontal cyclone by 96 hours while located at 58N-27.5W. For area of interest #1...broad low pressure consolidates just west of the Cayman Islands at 18 hours...the consolidated circulation shifts northwest into western Cuba by 66 hours...moves northwest into the eastern Gulf of Mexico and becomes absorbed by incoming cold front to the west by 120 hours. For area of interest #2...no tropical cyclone formation shown.

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