MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #16
*******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 MAY 29 2020 11:55 AM EDT...
Even though the Atlantic hurricane season does not start until June 1...continuing daily birdseye view posts on the Atlantic tropics due two areas of interest for tropical development...see area of interest sections below for additional details. Also see computer model summary section below...new to these birdseye view posts which summarized the computer model data used in making my forecast decisions.
AREA OF INTEREST #1...An upper trough in the western Atlantic to the northeast of the Caribbean and southeast of Bermuda has amplified further into a cut-off upper vortex as the longwave upper ridge that was over eastern North America is finally beginning to shift into the northwest Atlantic while pressing against the upper trough. The eastern divergence zone of the new upper vortex is producing a large comma shaped shower and thunderstorm mass as well as an ongoing surface trough of low pressure. The increased divergence on the east side of the upper vortex should result in a circular surface low pressure spin along the surface trough soon. Water temperatures in the area are running 24 to 26 deg C...at or just below the threshold for tropical development...but as infrared satellite shows the upper vortex is cold enough to support pockets of thunderstorm activity in the comma shaped cloud mass...so watching to see if a subtropical cyclone will form here. As of 0600Z this morning the National Hurricane Center placed a surface low at 25N-55W...and the ASCAT passes seem to agree with this position but also depicted that this low pressure spin is not circular...instead streteched north-to-south along the surface trough. High resolution GOES-16 visible satellite seems to suggest that a more circular low pressure spin might be trying to develop closer to the shower and thunderstorm activity near 28N-57.5W...which is where the upper divergence maximum of the upper vortex's east side is and also where I have been forecasting a surface low pressure spin to consolidate (based on the fact that the GFS has had the upper divergence maximum of the upper vortex at this location for a couple of days now). With the exception of May 27...the GFS has been depicting that this system's surface low pressure will remain weak thorugh its lifecycle...perhaps from the strong surface ridge to the north supported by the eastern upper convergence of the robust upper ridge moving into the northwestern Atlantic. The latest NAVGEM agrees with the GFS...while the Euro and CMC show a stronger surface low pressure. With a 50/50 split in these models...and also a 50/50 view on the current health of the system on satellite (comma shaped shower and thunderstorm mass underway...but a consolidated circular surface low pressure spin not yet defined)...I agree with the National Hurricane Center's 50% chance of subtropical cyclone formation in the next 24 hours. Regarding track...the surface low pressure and upper vortex should gradually shift northwestawrd and northward around the south and west sides of the upper ridge moving into the northwestern Atlantic as the ridge continues sliding east. I have nudged the longer range positions of this system southward due to the latest model consensus. At 48 hours I drop the odds of subtropical development to a very small 5% as the track will take this system to water temperatures in the low 20s of deg C...and the upper vortex by that time will at the 200 mb layer be at 1215 dekameters above sea level (would like to see the upper vortex be at 1200 or less at those water temperatures to believe the upper vortex is cold enough to support thunderstorm activity). By 72 hours...development should no longer be possible with even cooler water temperatures...and as the system at the surface and upper levels should become abosrbed by what is now a vigorous upper trough and surface frontal system over central Canada.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z May 30)...50% chance of subtropical cyclone formation (western Atlantic near 29N-57.5W)
IOH 48 Hr Outlook (1200Z May 31)...5% chance of subtropical cyclone formation (western Atlantic near 34N-57.5W)
IOH 72 Hr Outlook (1200Z Jun 1)...0% chance of subtropical cyclone formation (western Atlantic near 39N-56W)
AREA OF INTEREST #2...The thunderstorm activity in the eastern Pacific Ocean...to the southwest of Central America and south of southeastern Mexico...has started to redevelop as the upper ridge/outflow in the region has been able to re-expand due to the central United States upper vortex breaking up...with the naerby southwest lobe of the breakup retreating southwestward and away into northern Mexico while it orbits a longwave upper ridge building over western North America. Meanwhile the thunderstorm complex that was just east of Nicaragua 24 hours ago moved slowly ashore and broke up as expected. Once the aforementioned upper vorticity settles into northern Mexico after 24 hours...there will be room for the eastern Pacific upper ridge to expand toward the western Caribbean-Central America-southeastern Mexico region of the Atlantic basin. During the next 72 hours...computer models favor tropical cyclone development induced by the upper ridge on the eastern Pacific side...show I retain 0% odds of development on the Atlantic side as such an eastern Pacific circulation would dominate. With the exception of the CMC which is an eastern outlier...the models favor a more westward position of a broad surface low pressure in the Atlantic side...and this broad low pressure would be supported by the ongoing upper ridge/outflow and either be a seperate system after the eastern Pacific tropical cyclone moves over land (south-facing coasts of Mexico or Guatemala) and dissipates...or be the remains of the eastern Pacific cyclone after landfall. It also makes sense to drift the position of this area of interest westward in the updated outlook below as a strong potentially steering surface ridge develops over eastern North America in the western convergece zone of what is now the upper trough over central Canada. This westward drift keeps forecast positions over land on the Atlantic side...so I keep odds of development 0% through 96 hours...and finally raise them to 10% at 120 hours when finally reaching water (in the Bay of Campeche). I keep the odds of development on the Atlantic side at a low 10% as the model solutions are scattered and uncertain...and only the less reliable CMC and NAVGEM models explcitly depict tropical cyclone formation on the Atlantic side at this time. Meawhile one of the more reliable models...the GFS...completely shunts development on the Atlantic side and prefers to develop a second tropical cyclone in the eastern Pacific side as it shows the upper vorticity over northern Mexico in the long range diving southeastward (due to eastward shift of western North America upper ridge) and suppressing upper ridging/outflow on the Atlantic side.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z May 30)...0% chance of tropical cyclone formation (Honduras near 15N-87W)
IOH 48 Hr Outlook (1200Z May 31)...0% chance of tropical cyclone formation (north coast of Honduras near 16N-87W)
IOH 72 Hr Outlook (1200Z Jun 1)...0% chance of tropical cyclone formation (east coast of Belize near 16.5N-88.5W)
IOH 96 Hr Outlook (1200Z Jun 2)...0% chance of tropical cyclone formation (inland northern Guatemala/Mexico border near 17.5N-90W)
IOH 120 Hr Outlook (1200Z Jun 3)...10% chance of tropical cyclone formation (Mexico Bay of Campeche coast near 18.5N-91.5W)
...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 area of interest #1 develops a vigorous small surface low pressure in 24 hours and has it absorbed by incoming frontal low pressure system from central Canada in 72 hours...For area of interest #2 suggests possible eastern Pacific tropical cyclone at 42 hours that makes landfall on the south coasts of Honduras and Guatemala at 60 hours...then develops a broad low pressure area over Guatemala and Belize at 120 hours with possible tropical cyclone formation from this feature in the southern Gulf of Mexico in the longer range.
0000Z ECMWF Model Run...For area of interest #1 develops a vigorous small surface low pressure in 24 hours and has it absorbed by incoming frontal low pressure system from central Canada in 72 hours...For area of interest #2 develops weak tropical low pressure over the eastern Pacific in 48 hours that moves into southeastern Mexico and Guatemala after 72 hours...then develops a weak and broad surface low pressure over southeastern Mexico by 120 hours and gradually lifts it northward into the western Gulf of Mexico in the long range without showing tropical cyclone formation
0600Z GFS Model Run...For area of interest #1 shows a weak surface low pressure area from now through 72 hours when it is absorbed by incoming frontal low pressure system from central Canada...For area of interest #2 develops eastern Pacific low pressure/tropical cyclone beginning at 30 hours and has it stalling over Guatmela/southeastern Mexico coast by 60 to 78 hours...develops a second eastern Pacific tropical cyclone just offshore of southeastern Mexico in the long range without showing development on the Atlantic side.
0000Z NAVGEM Model Run...For area of interest #1 shows a weak surface low pressure area from now through 72 hours when it is absorbed by incoming frontal low pressure system from central Canada...For area of interest #2 develops eastern Pacific tropical cyclone beginning at 48 hours with landfall on southeastern Mexico and Guatemala coasts at 84 hours...remnant broad low pressure area of this cyclone crosses southeastern Mexico and develops into possible Atlantic-side tropical cyclone at Mexico Bay of Campeche coast by 120 hours...in longer range cyclone drifts southward and dissipates over Mexico while pivoting around broad low pressure area to the east that persists over Central America/Western Caribbean Sea