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 

  • NCHurricane2009


*******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 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 dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********

...FRIDAY JUNE 11 2021 5:38 PM EDT...

See area of interest #1 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 cold front trailing from the current northwest Atlantic frontal cyclone is stalling offshore of the northeast and mid-Atlantic US coasts. A weak surface low could form along the front...and offshore of the about 2 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 3 days...the upper trough currently over the northwestern US (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 I have not added a new area of interest for tropical development in regards to this situation.

AREA OF INTEREST #1...Over the last 12 hours...a surface tropical wave of low pressure that was in the vicinity of 91W longitude has evolved into a surface trough of low pressure in the Bay of Campeche...and more notably a thunderstorm-packed tropical low pressure spin in the eastern Pacific...while aided by the outflow of upper ridging centered over Guatemala and the northwest Caribbean. The eastern Pacific low pressure is moving slowly northeast toward the Oaxaca and Chiapas coasts of Mexico as steering mid-latitude surface ridging that would otherwise push this feature 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. Over the next 48 hours...the surface tropical wave of low pressure currently passing 82.5W longitude...currently highlighted as an area of interest for tropical development in the above charts...will also be likely be drawn toward the surface low pressure field underneath the upper outflow maximum...resulting in a merger between the eastern Pacific feature and tropical wave over the next 48 hours and in the vicinity of Guatemala or southeastern Mexico. The latest computer model runs remain in agreement that the merged feature will be lifted northward into the Bay of Campeche or western/central Gulf of Mexico in the long range with possible tropical cyclone formation. The mechanisms that could draw this system northward are as follows:

(1) The current upper trough over the northwest US...responsible for driving the current central US surface front...will merge with upper vorticity that has been lingering over the central US...resulting in a large upper trough dominating the eastern US in the long range. The western convergence zone of the large upper trough will support surface ridging over the central US

(2) Instead of having the central US surface ridge push the forecast tropical low pressure over Guatemala 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/southeastern 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.

My forecast track in the outlook below shows a slow west-northwest track of the current 82.5W tropical wave as it moves toward the field of low surface pressures over Guatemala over the next 48 hours...with the slow track and north angle being a result of the western extent of the steering Atlantic surface ridge being weakened by the current central US and western Atlantic surface frontal systems. After merging with the current eastern Pacific tropical disturbance by 48 hours...the forecast track is a continued slow west-northwest track into the Bay of Campeche....followed by a northward turn into the Bay of Campeche by 120 hours in accordance with the latest global model consensus. My peak 5-day odds of tropical cyclone formation are kept at a low 10%...lower than the NHC outlook as of this tropical development in this scenario will be strongly dependent on how exactly the forecast eastern US upper trough evolves in the long range...and model errors in the long range are always a possibility. For example if the upper trough does not amplify as much as currently forecast...this could result in a more hostile-for-development environment in the Gulf of Mexico (high wind shear and less upper divergence).

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

(1) I have removed Nicaragua and Honduras from heavy rainfall risk as thunderstorms have not increased over the area despite the current passage of the tropical wave in the area. This could be due to dry saharan air intrusion from the east (some beige tint on true-color visbile satellite imagery is visible over the eastern and central Caribbean)...and also as the upper outflow maximum of upper ridging in the area has settled further west.

(2) I have added Oaxaca and eastern Veracruz to the heavy rainfall risk as the eastern Pacific tropical disturbance is already spreading in thunderstorms and moisture into this area.

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

IOH 24 Hr Outlook (1800Z Jun 12)...0% chance of tropical cyclone formation (Nicaragua/Honduras border near 13.8N-86W)

IOH 48 Hr Outlook (1800Z Jun 13)...0% chance of tropical cyclone formation (Honduras/Guatemala border near 15N-89.2W)

IOH 72 Hr Outlook (1800Z Jun 14)...0% chance of tropical cyclone formation (southeastern Mexico near 16.5N-92W)

IOH 96 Hr Outlook (1800Z Jun 15)...10% chance of tropical cyclone formation (Bay of Campeche coast of Mexico near 18.5N-94W)

IOH 120 Hr Outlook (1800Z Jun 15)...10% chance of tropical cyclone formation (Bay of Campeche near 20N-94W)


Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (

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.

0000Z ECMWF Model Run...For area of interest #1...tropical cyclone formation shown in the western Gulf of Mexico near 23N-95W at 144 hours.

1200Z GFS Model Run...For area of interest #1...broad surface low coalesces over the eastern Bay of Campeche and Yucatan peninsula at 144 long range the northeast corner of the broad circulation consolidates into a tropical cyclone that moves north across the central Gulf of Mexico

1200Z NAVGEM Model Run...For area of interest #1...broad surface low coalesces over western Honduras and Guatemala at 120 hours...tropical cyclone formation suggested in long range as circulation moves northwest into Bay of Campeche

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