BIRDSEYE VIEW POSTS

Since 2012 on the now retired Weather Underground 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 at Yale Climate Connections via Disqus where the former Weather Underground community has moved to. Feel free to reply to me there, at my Disqus feed at this link, or via e-mail at IOHurricanes@outlook.com 

 
 
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MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #18

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


...SATURDAY JUNE 12 2021 7:16 PM EDT...

Satellite image as of 1940Z. Areas of interest circled in yellow are not mentioned in the NHC tropical weather outlook. Areas circled in a green dashed line are in the NHC 5-day tropical weather outlook. Areas circled in a solid green line are in the NHC 2-day tropical weather outlook:

NHC TAFB Surface Analysis 1200Z:

GFS Model Upper-Level Winds 1200Z:

Note that even though today is Saturday...I have not classified this update as a “weekend edition” as I have had time to compose and include the computer model summary section at the end of the update.


See area of interest #1 section below regarding the potential for tropical development in the southern Gulf of Mexico waters adjacent to southeastern Mexico over the next five days.


Elsewhere...the cold front trailing from the current northwest Atlantic frontal cyclone has stalled offshore of the US mid-Atlantic coast. A weak surface low could form along the front...and offshore of the Carolinas...over the next day or so as atmospheric lift is enhanced by the eastern divergence zone of a fragment of the current upper vorticity over the eastern US as that fragment settles over the Carolinas. However in about 2 days...the upper trough currently over central Canada (currently driving the central US surface front) 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 tropical cyclone development here is not expected.


AREA OF INTEREST #1...The tropical wave of low pressure that was crossing Nicaragua and Honduras has lost its identity to the stronger eastern Pacific tropical low pressure offshore of Oaxaca...tagged as Invest 93E...and surface trough of low pressure in the Bay of Campeche...tagged as Invest 92L...with numerous thunderstorm activity associated with both features over water and over parts of Oaxaca...Chiapas...Veracruz...Tabasco...and the Yucatan peninsula over the last day. Invests 92L and 93E are being supported by the outflow of upper ridging centered over Guatemala and the northwest Caribbean. Invest 93E’s thunderstorms have been displaced northeast of its surface spin as the outflow maximum of the upper ridge is off to its northeast...and the surface spin is drifting slowly northeast toward the Oaxaca and Chiapas coasts of Mexico as steering mid-latitude surface ridging that would otherwise push 93E westward is absent due to the presence of frontal systems over the central US and western Atlantic...and also while drawn toward the upper outflow maximum over Guatemala where surface pressures are being kept low.


Models agree on the large scale evolution of the atmosphere as follows:


(1) The current upper trough over the central Canada...responsible for driving the current central US surface front...will merge with upper vorticity that has been lingering over the eastern US...resulting in a large upper trough dominating the eastern US. The western convergence zone of the large upper trough will support surface ridging over the central US. At the same time the landfalling remnants of 93E will likely become a broad low pressure over Guatemala/SE Mexico while supported by the outflow maximum of the upper ridge in the region...which is forecast to keep its current position for a few days.


(2) Instead of having the central US surface ridge push the forecast tropical low pressure over Guatemala/SE Mexico westward...models have the large eastern US upper trough amplify southward into the western edge of the Gulf of Mexico due to amplification of adjacent western US warm upper ridging (in association with a forecast western North America vigorous frontal system's warm sector). This results in the Guatemala/SE Mexico tropical low pressure's reformation northward in the Gulf of Mexico while transitioning into a subtropical or tropical feature boosted by the eastern divergence zone of the amplifying upper trough.


The 1200Z and 0600Z runs of the GFS and 0000Z run of the NAVGEM suggest some short term development of Invest 92L while swung southwest into Veracruz by the forecast Guatemala/SE Mexico surface low...with the surface low undergoing its forecast and above-mentioned reformation northward into the Gulf of Mexico in the 4 to 5 day timeframe. One could interpret the GFS and 0600Z NAVGEM scenario as two seperate tropical cyclone events...or alternatively as one continuous event where a defined center of rotation cyclonically orbits southwest into the Veracruz coast of Mexico in the short term and then northward into the Gulf of Mexico in the long range. Due to the already organized thunderstorm squalls with 92L...in the updated outlook below I agree on the possibility of short-term development and have treated this situation as one slowly-evolving continuous event instead of two separate events. I assign a peak 15% odds of development in the short term as not all recent model runs showed this...and I have raised my long term peak odds of development to 30% due to the ongoing model consensus of an eastern US upper trough that becomes highly amplified which will keep shear low and upper divergence high in the Gulf of Mexico. In the medium term...I dip the odds to a minimum value of 10% due to the likelihood of the center of lowest pressure being over or near land.


Regarding the bulletins on the home page of this site...

(1) I will soon be adding a statement for Veracruz in regards to possible short-term tropical cyclone development


(2) I will be adding the Mexican provinces of Yucatan and Campeche to the heavy rainfall risk due to the updated forecast track in the outlook below

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

IOH 24 Hr Outlook (1800Z Jun 13)..5% chance of tropical cyclone formation (Bay of Campeche near 20N-94W)

IOH 48 Hr Outlook (1800Z Jun 14)...15% chance of tropical cyclone formation (offshore of Veracruz near 20N-95.5W)

IOH 72 Hr Outlook (1800Z Jun 15)...10% chance of tropical cyclone formation (coastal Veracruz near 19N-95.5W)

IOH 96 Hr Outlook (1800Z Jun 16)...10% chance of tropical cyclone formation (coastal Tabasco near 18.5N-93.5W)

IOH 120 Hr Outlook (1800Z Jun 17)...30% chance of tropical cyclone formation (Bay of Campeche near 21N-93.5W)


...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...broad surface low coalesces over the eastern Bay of Campeche and western Yucatan peninsula at 126 hours...shifts north across the western Gulf of Mexico in the long range while evolving into a tropical cyclone.

1200Z ECMWF Model Run...For area of interest #1...possible weak tropical cyclone formation shown in the Bay of Campeche near 20N-94W at 144 hours.


1200Z GFS Model Run...For area of interest #1...surface low forms in western Bay of Campeche near 19.5N-95.5W at 42 hours...surface low stationary thru 75 hours while evolving into a very compact tropical cyclone...drifts slowly SW into the Veracruz coast of Mexico thru 96 hours and dissipates while a broad circulation from SE Mexico emerges into the Bay of Campeche in its place...broad circulation shifts north across the western Gulf of Mexico in the long range while evolving into a tropical cyclone.


1200Z NAVGEM Model Run...For area of interest #1...broad surface low coalesces over NW Central America and Bay of Campeche at 108 hours...tropical cyclone formation suggested in long range as circulation moves NNW across western Gulf of Mexico

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