MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #15
*******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.**********
...WEDNESDAY JUNE 9 2021 8:45 PM EDT...
Tropical cyclone formation north of the Caribbean Islands....in association with an upper vortex...is no longer possible...see area of interest #1 section below for details. 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...a surface cold front is forecast to eject from the northeastern US and enter the northwest Atlantic in a couple of days. The CMC and ECMWF models have joined the GFS in forecasting the formation of a weak surface low along the tail end of the cold front...at a location offshore of the Carolinas...in about 4 days while atmospheric lift is enhanced by the eastern divergence zone of a fragment of the current upper vorticity over the central US as that fragment settles over the Carolinas. However in about 5 days...the upper trough currently over the western US coast is forecast to arrive in New England and Atlantic Canada...and support a broad frontal cyclonic system that would quickly absorb anything that develops offshore of the Carolinas. Therefore I have not added a new area of interest for tropical development in regards this situation.
AREA OF INTEREST #1...The western Atlantic upper vortex due north of the Caribbean Islands no longer has a surface trough under its eastern divergence zone...and continues to lack thunderstorms as well as it remains entangled with a lingering central Atlantic vortex to the east which is reducing the amount of divergence and keeping shear levels elevated. A cold front is forecast to eject from the northeastern US in a couple of days at about the same time wind shear may reduce and upper divergence increases when the two vortices gain more separation. However given the current lack of thunderstorms and low surface pressure...there will not be enough time for tropical development as the incoming cold front to the northwest develops a frontal cyclone that dominates the region by day 4. This is my final statement on this area of interest on this blog.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Jun 10)...0% chance of tropical cyclone formation (western Atlantic near 25N-62.5W)
AREA OF INTEREST #2...Showers and thunderstorms in the southern Caribbean Sea are increasing as the central Caribbean upper vorticity that had dominated the region has dissipated...and in its wake is split flow upper divergence between the south side of the upper vortex tied to area of interest #1 and southeast side of upper ridging that has entered the NW Caribbean from the Gulf of Mexico. A surface tropical wave of low pressure in the Caribbean that was crossing 71W longitude as of 1200Z earlier today will enter the supportive upper divergence zone in the next 24 hours...and it is possible by Friday and Saturday that the tropical wave strengthens into a thunderstorm-packed broad tropical low pressure as it moves toward Central America. 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 continue to forecast low 10% odds of tropical cyclone formation before this system makes landfall in Central America as none of the computer models currently show tropical cyclone development in the short-term. The NHC has also lowered odds of development to 10% as of this writing.
(3) As this broad system moves west-northwest across Central America and then into southeast Mexico by 5 to 7 days...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 10)...0% chance of tropical cyclone formation (southern Caribbean Sea near 11.5N-76W)
IOH 48 Hr Outlook (1800Z Jun 11)...10% chance of tropical cyclone formation (southern Caribbean Sea near 12.5N-81W)
IOH 72 Hr Outlook (1800Z Jun 12)...10% chance of tropical cyclone formation (just inland from the east coast of Nicaragua near 13.5N-84.5W)
IOH 96 Hr Outlook (1800Z Jun 13)...0% chance of tropical cyclone formation (western Honduras near 14.5N-88W)
IOH 120 Hr Outlook (1800Z Jun 14)...0% chance of tropical cyclone formation (Guatemala/Mexico Border near 16N-91W)
...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 the Bay of Campeche at 114 hours. Elsewhere...weak surface low at tail end of frontal boundary develops offshore of the Carolinas at 108 hours...absorbed by frontal cyclone centered over eastern Canada before having a chance to develop by 126 hours.
1200Z ECMWF Model Run...For area of interest #1...no tropical cyclone formation shown. For area of interest #2...broad surface low pressure consolidates over the Bay of Campeche at 144 hours. Elsewhere...weak surface low at tail end of frontal boundary develops offshore of the Carolinas at 96 hours...absorbed by frontal cyclone centered over eastern Canada before having a chance to develop by 120 hours.
1200Z GFS Model Run...For areas of interest #1 and #2...no tropical cyclone formation shown. Elsewhere...weak surface low at tail end of frontal boundary develops offshore of South Carolina at 96 hours...absorbed by frontal cyclone centered over eastern Canada before having a chance to develop by 126 hours.
1200Z NAVGEM Model Run...For areas of interest #1 and #2...no tropical cyclone formation shown.