MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #111

*******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.**********

...THURSDAY SEPTEMBER 3 2020 2:27 PM EDT...

See Tropical Storm Nana and Tropical Depression Omar sections below for the two currently active tropical cyclones in the Atlantic basin. See area of interest #1 and #2 sections below for tropical low pressure areas being watched for development. Elsewhere...models generally agree that another vigorous tropical wave of low pressure capable of development will emerge from western Africa in about 3 days...see area of interest #3 section below for details.

TROPICAL STORM NANA...As noted in special update #110A from the overnight...Nana managed to become a minimal hurricane just before landfall in Belize. Due to the landfall Nana is now a weak tropical storm and is moving west-southwestward across Guatemala...the south angle in track being present as Nana has been a sufficiently strong/tall system to be dragged by upper northeasterly winds induced by upper vorticity that has been approaching from the east. My updated forecast track below is an extrapolation of the current west-southwest motion...which will bring what will be the remmant circulation of Nana into the eastern Pacific just after 24 hours. None of the computer models in the model summary below forecast Nana to regenerate as an eastern Pacific tropical cyclone...instead dissipating the remnant low before it reaches the eastern Pacific. However the National Hurricane Center is monitoring Nana for possible regeneration in the eastern Pacific. Because the eastern Pacific is outside the scope of the Atlantic basin coverage provided on this site...visit the National Hurricane Center eastern Pacific tropical weather outlook at hurricanes.gov for the latest on a technical discussion on the remannts of Nana. I plan this to be my final statement on this blog on Nana as the tropical storm will soon weaken to a remnant low pressure...but I will mention potential impacts from the remnants of Nana on the home page bulletins of this site should the remnants survive and affect the south-facing eastern Pacific coast of Mexico in the coming days.

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

0 Hr Position (1200Z Sep 3)...45 mph maximum sustained wind tropical storm centered over northern Guatemala at the northern Belize/Guatemala border at 16.4N-90.3W

IOH 24 Hr Forecast (1200Z Sep 4)...Remnant low pressure located on the south-facing eastern Pacific coast of Chiapas province of southeastern Meixco at 16N-94W

TROPICAL DEPRESSION OMAR...As it has done over the last 48 hours...Omar has been hanging on as a tropical cyclone while blasted by northwesterly wind shear on the west side of a shortwave upper trough. Omar has been stuck beneath the west side of this trough whle continuing to be gravitated toward the frontal low pressure to the east that has been supported by the eastern divergence zone of the trough. Once more I have nudged my forecast points southward as satellite animation shows no northward angle in track yet beginning...but this shift in track is smaller than the shift I made yesterday. Eventually a northward bend in track is expected as both Omar and the frontal low pressure it has been following will run into the northwest side of the Atlantic surface subtropical ridge...but perhaps the lack of a northward turn in Omar's track so far has been caused by the northerly flow in the southwest quadrant of the frontal low pressure. The southward shift in my forecast track is just enough to keep Omar over 26+ deg C waters for 24 more hours...so I have delayed the transition to a remnant low pressure for another 24 hours. By 48 hours the shear direction will switch from northerly to southwesterly as the upper trough currently over central Canada finally approaches. However the southward shift in my forecast track places Omar just south of the southwesterly upper winds at 48 hours...so it wouldn't suprrise me if Omar becomes a tropical storm again. I also wouldn't be suprised if Omar regains tropical storm status before 48 hours as the tropical depression has been continously firing strong thunderstorm bursts near the center despite the current northwesterly shear.

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

0 Hr Position (1200Z Sep 3)...35 mph maximum sustained wind tropical depression centered in the western Atlantic at 35.9N-61.1W

IOH 24 Hr Forecast (1200Z Sep 4)...35 mph maximum sustained wind tropical depression centered in the northwestern Atlantic at 36N-57.5W

IOH 48 Hr Forecast (1200Z Sep 5)...35 mph maximum sustained wind tropical depression centered in the northwestern Atlantic at 39.5N-54.5W

IOH 72 Hr Forecast (1200Z Sep 6)...Absorbed by cold front while passing 45N-49W

AREA OF INTEREST #1...The tropical wave of low pressure in the far eastern tropical Atlantic continues merging with a low pressure area near 12.5N-22.5W. The merger between these two systems is creating a large area of curved thunderstorm bands to the south of the Republic of Cabo Verde Islands. My updated outlook below is a continuity of the previous one as the computer models and current satelltie animation suggest not much has changed. The models agree that this disturbance and tropical low pressure in area of interest #2 will orbit each other in a fujiwhara type of interaction...keeping area of interest #2 generally stationary for a few days while this system tracks more northward in its westward track. The disagreement in the modeling has more to do with which feature will develop...with the ECMWF developing area of interest #2 and this system...while the CMC...ECMWF...and NAVGEM prefer this disturbance only. My forecast track in the outlook below between 24 to 48 hours bends the track of this system northward as it undergoes a fujiwhara interaction with area of interest #2...followed by a more westward track resuming after the intraction is complete. I have increased peak 5-day odds of tropical cyclone formation to 60%...which is not quiet as high as the National Hurricane Center's peak odds in their tropical weather outlook. This is because there is a batch of dry saharan air just north of this system...and I have some uncertainty as to how much this dry air will affect this system as this hurricane season has had a recent history of no development in the eastern Atlantic from the dry saharan air layer. My short-term odds at a very low 10% through 48 hours to give time for this large broad disturbance to potentially absorb area of interest #2...and then consolidate after the potential absorption. This also gives time for any dry saharan air intrusions to be mixed out. This thinking is in agreement with the latest model guidance which generally agrees with develoipng this system toward 120 hours instead of immediately. On a final note...this disturbance is forecast to be beneath rather favorable upper winds by 120 hours while in a vast area of low shear and upper outflow between the current central Atlantic upper vorticity and a large upper vortex to cut-off from the south side of the current northeast Atlantic upper trough...so if this system develops it could become a strong tropical cyclone.

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

IOH 24 Hr Outlook (1200Z Sep 4)...10% chance of tropical cyclone formation (southwest of the Republic of Cabo Verde Islands near 13N-27.5W)

IOH 48 Hr Outlook (1200Z Sep 5)...10% chance of tropical cyclone formation (tropical Atlantic near 14.5N-32.5W)

IOH 72 Hr Outlook (1200Z Sep 6)...30% chance of tropical cyclone formation (tropical Atlantic near 15N-37.5W)

IOH 96 Hr Outlook (1200Z Sep 7)...50% chance of tropical cyclone formation (tropical Atlantic near 15.5N-42.5W)

IOH 120 Hr Outlook (1200Z Sep 8)...60% chance of tropical cyclone formation (tropical Atlantic near 16N-47.5W)

AREA OF INTEREST #2...A tropical low pressure spin has persists near 13N-36W. Both this tropical low pressure and the parent tropical wave at 45W longitude that spawned this low pressure have become generally stationary while gravitated toward the low pressure field of the much larger disturbance in area of interest #1. The thunderstorms continue to be sheared off to the northwest quadrant of the low pressure spin due to easterly upper winds on the south side of the tropical upper ridge in the region...normally shear does not occur here during the peak of the hurricane season in September as tropical systems tend to move westward around the Atlantic subtropical ridge and thus keep up with the upper easterly winds. Instead this low pressure swirl is generally stationary and drifting east-northeastward while gravitated toward the much larger low pressure system mentioned in area of interest #1. Because this system is the smaller of the two disturbances and is getting sheared due to its generally stationary motion...I have only low 10% odds of tropical cyclone formation while assuming the larger disturbance in area of interest #1 will absorb it before it has a chance to develop.

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

IOH 24 Hr Outlook (1200Z Sep 4)...10% chance of tropical cyclone formation (tropical Atlantic near 13.5N-36W)

IOH 48 Hr Outlook (1200Z Sep 5)...0% chance of tropical cyclone formation (absorbed by area of interest #1 near 13.5N-35.5W)

AREA OF INTEREST #3...Computer models for two days in a row agree that a well-organized tropical wave of low pressure will emerge from western Africa in the timframe that is now about three days from now and rapidly develop into a tropical cyclone. Based on the model initializations and satellite imagery...it appears the wave is currently over northern Mali in the vicinity of 20N-2W with limited thunderstorm activity at the present time. Given the strong model signals...the National Hurricane Center has introduced this tropical wave into their tropical weather outlook. The forecast positions in the outlook below is based on the model consensus that shows a west-southwestward tracking commencing from northern Mali in the short-term around the southeast side of the Atlantic subtropical ridge. In the long term...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 central 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 potnetially draws this system more northward....and if this system indeed does quickly develop as the models show it could become strong/tall enough to be guided more northward by the southerly upper flow ahead of the vortex. Given the model projections...we could be in for an unusal tropical cyclone event that passes directly over or northeast of the Republic of Cabo Verde Islands instead of south of the islands as we usually see...therefore I have begun statements on the home page bulletins of this site for the Republic of Cabo Verde Islands in regards to this system.

Given the strong model consensus on developing this system...I give a medium peak of 50% odds of tropical cyclone formation for the next 5 days (120 hours). I have not gone with high odds at this time as the more north position and track of this system could expose it to dry saharan air...and this system has yet to develop widespread thunderstorms.

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

IOH 24 Hr Outlook (1200Z Sep 4)...0% chance of tropical cyclone formation (eastern Mauritania near 19N-7W)

IOH 48 Hr Outlook (1200Z Sep 5)...0% chance of tropical cyclone formation (western Mauritania near 18N-12W)

IOH 72 Hr Outlook (1200Z Sep 6)...10% chance of tropical cyclone formation (just offshore of Mauritania near 17.5N-17W)

IOH 96 Hr Outlook (1200Z Sep 7)...35% chance of tropical cyclone formation (northeast of the Republic of Cabo Verde Islands near 18.5N-22.5W)

IOH 120 Hr Outlook (1200Z Sep 8)...50% chance of tropical cyclone formation (tropical Atlantic near 19.8N-25W)

...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 Tropical Storm Nana...loses its identity over southern Chiapas province in Mexico by 18 hours. For Tropical Depression Omar...opens to a surface trough near 38N-57W in 60 hours. For area of interest #1...tropical cyclone formation suggested near 19N-47W at 150 hours. For area of interest #2...generally stationary while area of interest #1 passes to the north...absorbed into the east side of area of interest #1 in 96 hours. For area of interest #3...tropical cyclone formation suggested east of the Republic of Cabo Verde Islands in 102 hours.

0000Z ECMWF Model Run...For Tropical Storm Nana...loses its identity over western Guatemala in the next 24 hours. For Tropical Depression Omar...weakens to a surface trough near 41N-54W in 72 hours. For area of interest #1...tropical cyclone formation suggested near 19.5N-53W at 120 hours. For area of interest #2...generally stationary through 72 hours while area of interest #1 passes to the north...tropical cyclone formation suggested near 13.5N-40.5W at 120 hours. For area of interest #3...tropical cyclone formation suggested just east-northeast of the Republic of Cabo Verde Islands at 17.5N-20.5W in 96 hours...located at 22.5N-23W at 120 hours.

0600Z GFS Model Run...For Tropical Storm Nana...loses its identity over southern Chiapas province in Mexico by 12 hours. For Tropical Depression Omar...opens to a surface trough near 40.5N-52.5W in 66 hours. For area of interest #1...tropical cyclone formation suggested near 17.5N-47.5W in 120 hours. For area of interest #2...generally stationary through 84 hours while area of interest #1 passes to the north...in long range begins to drift westward around 12.5N latitude while located between areas of interest #1 and #3 but no tropical cyclone formation shown. For area of interest #3...tropical cyclone formation suggested just offshore of western Africa near 14N-19W in 72 hours...becomes a strong tropical cyclone while passing over the northern Republic of Cabo Verde Islands in 120 hours.

0600Z NAVGEM Model Run... For Tropical Storm Nana...loses identity over western Guatemala/Mexico border in 18 hours. For Tropical Depression Omar...opens to a surface trough near 36N-59W in 30 hours. For area of interest #1...tropical cyclone formation suggested near 15N-34W in 120 hours. For area of interest #2...shown to be generally stationary and then absorbed into the south side of area of interest #1 in 66 hours. For area of interest #3...tropical cyclone formation suggested just offshore of western Africa near 17N-17.5W in 114 hours.