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 #113

Updated: Sep 7

*******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 SEPTEMBER 6 2020 12:21 AM EDT...

Satellite Image from 0310Z (red indicates tropical cyclone or remnants of tropical cyclone...with O marking remnants of Omar...N/J marking the remnants of Nana which have regenerated into eastern Pacific Tropical Storm Julio. Green indicates an area of interest in the National Hurricane Center Tropical Weather Outlook. Yellow indicates an area of interest not in the National Hurricane Center Tropical Weather Outlook.):


NHC TAFB Surface Analysis 0000Z:

GFS Model Upper Level Winds 1800Z:

See remnants of Omar section below for a final statement on this system. See area of interest sections below for all areas of interest being monitored for tropical cyclone formation. Elsewhere...models indicate another vigorous tropical wave from Africa may become another area of interest for tropical development as it emerges into the eastern tropical Atlantic in about 4 to 5 days:

TROPICAL DEPRESSION OMAR (RECENTLY DOWNGRADED TO REMNANT LOW)...Despite the shortwave upper trough to the east moving away...Omar has remained under northerly shear while earlier failing to move northward away from upper northerlies streaming into western Atlantic upper vorticity that lies to the south. This afternoon Omar finally began moving northward around the Atlantic subtropical surface ridge...resulting in the surface swirl of low pressure separating from the thunderstorms sheared to the south of the center. With no new thunderstorm activity near the swirl...the National Hurricane Center downgraded Omar to a remnant low as of 5 PM EDT. The remnant low has no chance to regenerate into a tropical cyclone while soon to be absorbed by a cold front driven by the eastern Canada frontal cyclone and also as it moves into cooler water. Many of today’s model runs suggested the remnant low may persist along the front while moving into the open far North Atlantic while supported by the eastern divergence zone of the upper trough also approaching from eastern Canada. This is my final statement on Omar on this blog as it is no longer a tropical system.

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

0 Hr Position (1800Z Sep 5)...35 mph maximum sustained wind tropical depression centered in the northwestern Atlantic at 38N-56W

IOH 24 Hr Forecast (1800Z Sep 6)...Absorbed by cold front while passing 43N-52W

AREA OF INTEREST #1...The tropical wave of low pressure in the eastern tropical Atlantic has only been slowly organizing while still absorbing another low pressure immediately to the west. The western low was appearing as a second hook of thunderstorm not concentric with the other bands tied to this wave. But recently as of this late afternoon and as we head into the evening...the absorption appears to be complete as all thunderstorm bands are becoming concentric about this tropical wave. Even the other tropical low pressure to the southwest...area of interest #2...appears to have been absorbed into this tropical wave while its satellite appearance had degenerated into being one of the outer bands of this tropical wave. Based on the curvature of all bands...I estimate the lowest pressure of the wave is near 18N-32.5W

My updated positions in the outlook below are adjusted northward given the current estimated location of the lowest pressure. Many recent model runs show a slow down in the westward track of this system...perhaps from low surface pressures that will weaken the south side of the steering Atlantic subtropical ridge...to be created by the eastern divergence zones of upper vorticity soon to be cut-off in the northeast Atlantic and upper vorticity in the western Atlantic. Also the tug from the tropical wave currently emerging from western Africa...area of interest #3...may also play a role in slowing the westward progress of this system. Thus I show a slower forward speed in the outlook below in between 48 and 96 hours...with some increase in forward speed by 120 hours as the south side of the Atlantic subtropical ridge recovers once the cut off upper vorticity to the northeast and west begins to weaken. I have some northward angle in track at 48+ hours as this system likely becomes a strong/tall enough tropical cyclone that becomes dragged by the upper vorticity to the west..but by 120 hours I reduce the north angle a touch with the possibility that area of interest #3 nears and tries to drag this system more southward. I have only slightly raised my peak 5 day odds of tropical cyclone formation to 65% due to the current limited thunderstorm intensity...perhaps from the dry saharan air to the north...and also as the GFS model shows less separation between the upper vorticity to the northeast and west...increasing the chances this system gets exposed to some westerly shear. The GFS shows a gap between the two upper vorticity lobes by 120 hours as the two lobes begin to weaken...which may reduce the shear potential...and so this is when I raise the odds to the 65%.

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

IOH 24 Hr Outlook (1800Z Sep 6)...20% chance of tropical cyclone formation (tropical Atlantic near 18N-37.5W)

IOH 48 Hr Outlook (1800Z Sep 7)...40% chance of tropical cyclone formation (tropical Atlantic near 18N-41.5W

IOH 72 Hr Outlook (1800Z Sep 8)...60% chance of tropical cyclone formation (tropical Atlantic near 19N-43.5W)

IOH 96 Hr Outlook (1800Z Sep 9)...60% chance of tropical cyclone formation (tropical Atlantic near 20N-45.5W)

IOH 120 Hr Outlook (1800Z Sep 10)...65% chance of tropical cyclone formation (tropical Atlantic near 21N-48.5W)

AREA OF INTEREST #2...The tropical low pressure in the central tropical Atlantic has been absorbed into the southwest side of the tropical wave approaching from the east...area of interest #1. This feature has been removed from the National Hurricane Center tropical weather outlook...and this is my final statement on this feature on this blog.

AREA OF INTEREST #3... The tropical wave of low pressure over interior Western Africa is producing stronger thunderstorms in the vicinity of 15N-12.5W. As a result I have shifted my updated outlook forecast positions southward compared to my previous outlook. I still forecast a more north bend in track to occur in the time that is now between 24 and 48 hours as the south side of the northeast Atlantic upper trough is forecast to cut-off into a large vortex thanks to amplification of adjacent high latitude upper ridging to be kikced off by warm air advection ahead of the frontal cyclone currently over eastern Canada. The eastern divergence zone of this vortex will create a pocket of low pressure on the southeast side of the Atlantic subtropical ridge that potentially draws this system more northward in track....and if this system indeed does quickly develop as some models show it could become strong/tall enough to be guided more northward by the southerly upper flow ahead of the vortex. After 48 hours I now bend the track more westward than I previously forecasted as the latest GFS shows the upper vortex not reaching as far south. I also slow the forward speed between 48 and 96 as the aforementioned northeast Atlantic upper vortex and also upper vorticity in the west Atlantic are forecast to weaken the south side of the Atlantic subtropical ridge...see area of interest #1 section. I accelerate the forward speed by 120 hours as the Atlantic subtropical ridge recovers while the upper vorticity weakens.

We could be in for an unusual tropical cyclone event that passes directly over the Republic of Cabo Verde Islands by 48 hours instead of south of the islands as we usually see...therefore I am continuing statements on the home page bulletins of this site for the Republic of Cabo Verde Islands in regards to this system. I have increased my peak 5 day odds of tropical cyclone formation to 70% given the increased thunderstorms and further south position of this tropical wave which places it further away from the dry saharan air layer. However the 70% is placed only toward day 5 as the thunderstorms are not yet well organized with curved banding features.

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

IOH 24 Hr Outlook (1800Z Sep 6)...0% chance of tropical cyclone formation (just offshore of Africa near 15N-17.5W)

IOH 48 Hr Outlook (1800Z Sep 7)...20% chance of tropical cyclone formation (over the Republic of Cabo Verde Islands near 16.5N-22.5W)

IOH 72 Hr Outlook (1800Z Sep 8)...40% chance of tropical cyclone formation (just west of the Republic of Cabo Verde Islands near 17N-25.5W)

IOH 96 Hr Outlook (1800Z Sep 9)...55% chance of tropical cyclone formation (tropical Atlantic near 17.5N-28.5W)

IOH 120 Hr Outlook (1800Z Sep 9)...70% chance of tropical cyclone formation (tropical Atlantic near 18N-33.5W)

AREA OF INTEREST #4...Thunderstorm activity in the central Caribbean Sea is much less than yesterday as the thunderstorm complex in the area has diminished and the tropical wave coming in from the east has not added much activity thus far. Despite this the National Hurricane Center has added the tropical wave to their tropical weather outlook...but I have dropped odds of development due to the lackluster thunderstorm activity. I forecast this system to move slowly for the next 48 hours while the tail end of the front absorbing Omar weakens the surface easterly steering flow...then I forecast a faster west-northwest to northwest track as the surface ridge currently over the eastern United States passes north of this system. The northwest bend in track by 120 hours I expect will also be from a front in the Gulf of Mexico to be supported by a sharp upper trough to reach the central Unites States by that timeframe. I will also note that my forecast track points are nudged northward as the tiny amount of thunderstorms produced by the tropical wave are at 16N latitude. On this forecast track...this system will be below favorable upper winds between east and west fractures of upper vorticity that has been spanning the Caribbean and western Atlantic for the next 48 hours. After that time...this disturbance will catch up to less favorable upper winds below the western fracture of the upper vorticity where upper outflow may become constricted...but I don’t drop the odds of development to 0% as the GFS shows the upper vorticity to be weak. But given the less favorable upper wind outlook after 48 hours....the home page bulletins of this site only mentions Jamaica in relation to this disturbance as the Cayman Islands and beyond will be covered by the unfavorable upper vorticity.

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

IOH 24 Hr Outlook (1800Z Sep 6)...5% chance of tropical cyclone formation (central Caribbean Sea near 16.5N-73W)

IOH 48 Hr Outlook (1800Z Sep 7)...10% chance of tropical cyclone formation (just southeast of Jamaica near 17N-76W)

IOH 72 Hr Outlook (1800Z Sep 8)...10% chance of tropical cyclone formation (just west of Jamaica and just south of the Cayman Islands near 17.5N-80W)

IOH 96 Hr Outlook (1800Z Sep 9)...10% chance of tropical cyclone formation (northwestern Caribbean Sea to the west of the Cayman Islands and south of western Cuba near 19N-84W)

IOH 120 Hr Outlook (1800Z Sep 10)...10% chance of tropical cyclone formation (southeastern Gulf of Mexico near 21.5N-86W)

...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)

1200Z CMC Model Run...For Tropical Depression Omar...merges with front from eastern Canada frontal cyclone by 24 hours...persists as a remnant frontal low pressure that accelerates northeastward...remnant frontal low loses identity near 50N-35W at 54 hours. For area of interest #1...tropical cyclone formation suggested near 16N-43W in 60 hours...located at 19N-46W at 120 hours. For area of interest #2...becomes immediately absorbed into area of interest #1. For area of interest #3...organizes into a tropical low pressure just east of the Republic of Cabo Verde Islands at 48 hours...no tropical cyclone formation shown thru 120 hours as tropical low pressure moves westward away from the islands. For area of interest #4...no tropical cyclone formation shown.

1200Z ECMWF Model Run....For Tropical Depression Omar...merges with front from eastern Canada frontal cyclone by 24 hours...persists as a remnant frontal low pressure that accelerates northeastward...remnant frontal low loses identity near 50N-30W at 72 hours. For area of interest #1...tropical cyclone formation suggested near 17.5N-43.5W at 72 hours...located at 17.5N-48W at 120 hours. For area of interest #2...immediately absorbed into area of interest #1. For area of interest #3...tropical cyclone formation suggested over the northeastern Republic of Cabo Verde Islands at 72 hours...located at 19N-35W at 120 hours. For area of interest #4...no tropical cyclone formation shown. Elsewhere...tropical wave emerges from Western Africa in 120 hours...tropical cyclone formation suggested near 12.5N-20W in 144 hours.

1200Z GFS Model Run...For Tropical Depression Omar...merges with front from eastern Canada frontal cyclone by 24 hours...persists as a remnant frontal low pressure that accelerates northeastward...remnant frontal low loses identity near 50N-30W at 60 hours. For area of interest #1...tropical cyclone formation suggested near 16.5N-41W in 48 hours...located at 19N-51W at 120 hours. For area of interest #2...immediately absorbed into area of interest #1. For area of interest #3...tropical cyclone formation suggested just west of the Republic of Cabo Verde Islands in 78 hours...becomes a strengthening tropical cyclone at 15N-35W at 120 hours. For area of interest #4...no tropical cyclone formation shown. Elsewhere...tropical wave emerges from Western Africa in 96 hours...tropical cyclone formation suggested near 12.5N-21W at 120 hours.

0600Z NAVGEM Model Run...For Tropical Depression Omar...merges with front from eastern Canada frontal cyclone by 24 hours...persists as a remnant frontal low pressure that drifts northeastward...remnant frontal low loses identity near 44N-45W at 90 hours. For area of interest #1...tropical cyclone formation suggested near 17.5N-35W at 30 hours...located at 16.5N-41W at 120 hours. For area of interest #2...immediately absorbed by area of interest #1. For area of interest #3...tropical cyclone formation suggested near 17N-20W in 66 hours...passed over northern Republic or Cabo Verde Islands in 90 hours..located just northwest of the Islands in 120 hours. For area of interest #4...no tropical cyclone formation suggested. Elsewhere...strong tropical wave exits Western Africa at 144 hours.

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