MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #14
*******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.**********
...TUESDAY JUNE 8 2021 9:20 PM EDT...
See area of interest #1 section below regarding the potential tropical development between Bermuda and the northern Caribbean Islands over the next five days. See area of interest #2 section below regarding the potential for tropical development in the southern Gulf of Mexico and Caribbean waters adjacent to Central America and southeastern Mexico over the next week.
Elsewhere...the GFS model had recently trended with a slower eastward progression of the current upper vorticity over the central US...resulting in a larger separation between the upper vorticity and the west Atlantic vortex associated with area of interest #1. The resulting upper-level flow on the east side of the upper vorticity....and offshore of the eastern US...would have more divergence and lower wind shear in this scenario. Therefore tropical development along the tail end of the surface front to emerge offshore from the northeast US in 3 to 5 days...at a location offshore of the Carolinas...is a possibility. Whether this scenario actually occurs is strongly dependent on how the current central US upper vorticity evolves...which in turn is strongly dependent on the exact evolution of adjacent upstream upper ridges and troughs over western and northern North America in the coming days. Waiting to see if this GFs model solution persists...and if other models agree...before declaring a new area of interest for the waters just offshore of the Carolinas.
AREA OF INTEREST #1...A weak surface trough of low pressure north of the Caribbean Islands near 65W longitude was added onto the NHC TAFB surface analysis at 1200Z earlier today...supported by the eastern divergence zone of the upper vortex currently in the west Atlantic. Watching to see if thunderstorm activity develops with this feature in the coming days....however the only model that showed tropical development here...the GFS...no longer shows development! The latest GFS runs show less separation between the aforementioned upper vortex and another lingering upper vortex to the east for the next 48 hours....with the resulting upper flow being less divergent (i.e. less potential for thunderstorms) and more shearing (i.e. less favorable for tropical cyclone development). Therefore I have lowered my peak odds of development to 5%....and only show odds above 0% at 96 hours when the GFS shows more separation between the two upper vortices. A northward track is likely to begin by days 4 and 5 as a North Atlantic/eastern Canada upper trough is forecast to amplify southward and gradually erode the west extent of the Atlantic surface ridge...while driving a frontal cyclone to exit from Atlantic Canada by day 2...and by days 3 to 5 while driving a surface front to eject from the northeast US. Beyond day 4...conditions for tropical development will be less favorable as the north track will take this system to waters below 26 deg C and as this system would be absorbed into a frontal cyclone forecast to develop along the front that ejects from the northeastern US.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jun 9)...0% chance of tropical cyclone formation (western Atlantic near 25N-65W)
IOH 48 Hr Outlook (1800Z Jun 10)...0% chance of tropical cyclone formation (western Atlantic near 25N-62.5W)
IOH 72 Hr Outlook (1800Z Jun 11)...0% chance of tropical cyclone formation (western Atlantic near 25N-61W)
IOH 96 Hr Outlook (1800Z Jun 12)...5% chance of tropical cyclone formation (western Atlantic near 27.5N-59W)
IOH 120 Hr Outlook (1800Z Jun 13)...0% chance of tropical cyclone formation (absorbed by frontal cyclone near 32.5N-55W)
AREA OF INTEREST #2...Computer models remain in agreement on the eventual dissipation of the current Caribbean cold core upper vorticity as it remains cut-off from mid-latitude cold air. The vorticity is forecast to be replaced by the warm core upper ridging currently over the eastern Gulf of Mexico. The low shear and outflow of the upper ridging will make conditions more conducive for the lowering of surface pressures and tropical development across Central America and the Caribbean. By Friday and Saturday...the tropical wave of low pressure currently over the eastern Caribbean is expected to arrive in the central Caribbean...about the time that upper divergence may be further enhanced by split flow between the south side of the upper vorticity associated with area of interest #1 and south side of the upper ridging to expand into the Caribbean from the eastern Gulf. Therefore the tropical wave may strengthen into a broad tropical low pressure. Here are the key takeaways:
(1) Any broad low pressure that develops in the southern Caribbean is likely to slowly advance west-northwest into Central America Saturday and Sunday as the west extent of the steering Atlantic surface ridge weakens when a frontal system is forecast to eject from the northeast US. Heavy rainfall will be possible over parts of Central America this weekend and into next week per the bulletins on the home page of this site....regardless of tropical cyclone development or not.
(2) I currently forecast low 10% odds of tropical cyclone formation by day 5...lower than the NHC 5-day outlook...as none of the computer models currently show tropical cyclone development over the next 7 days.
(3) As this broad system moves west-northwest across Central America and toward southeast Mexico this weekend and into next week...it will be hard to say if and when a tropical cyclone would ultimately consolidate within the broad circulation and over the adjacent eastern Pacific waters...or over the adjacent western Caribbean and southern Gulf of Mexico waters...or perhaps over both basins (i.e. an eastern Pacific tropical cyclone that develops in the long range...which then crosses over to the southern Gulf of Mexico...or alternatively a pair of twin tropical cyclones...one over the eastern Pacific...and another over the western Caribbean or southern Gulf of Mexico).
IOH 24 Hr Outlook (1800Z Jun 9)...0% chance of tropical cyclone formation (northwest coast of Venezuela near 11N-70W)
IOH 48 Hr Outlook (1800Z Jun 10)...0% chance of tropical cyclone formation (southern Caribbean Sea near 11.5N-75W)
IOH 72 Hr Outlook (1800Z Jun 11)...10% chance of tropical cyclone formation (southern Caribbean Sea near 12.5N-80W)
IOH 96 Hr Outlook (1800Z Jun 12)...10% chance of tropical cyclone formation (east coast of Nicaragua near 13.5N-84W)
IOH 120 Hr Outlook (1800Z Jun 13)...0% chance of tropical cyclone formation (Honduras near 14N-87.5W)
...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 area of interest #1...no tropical cyclone formation shown. For area of interest #2...broad surface low pressure consolidates over southeastern Mexico and northwestern Central America by 156 hours.
0000Z ECMWF Model Run...For areas of interest #1 and #2...no tropical cyclone formation shown.
1200Z GFS Model Run...For areas of interest #1 and #2...no tropical cyclone formation shown. Elsewhere...surface low at tail end of frontal boundary becomes defined offshore of the Carolinas at 120 hours with possible tropical development.
1200Z NAVGEM Model Run... For area of interest #1...no tropical cyclone formation shown. For area of interest #2...tropical low forms just east of Nicaragua at 144 hours and makes landfall on the Nicaragua coast at 156 hours.