BIRDSEYE VIEW POSTS

Since 2012 on the Weather Underground (www.wunderground.com) 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 via Disqus on Weather Underground at www.wunderground.com/cat6. You can see my Disqus feed at this link for my latest comments. Feel free to reply to me with your disqus account or e-mail at IOHurricanes@outlook.com 

 
 
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MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #20

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


...MONDAY JUNE 14 2021 9:40 PM EDT...

The Atlantic tropics are becoming unusually busy for mid-June. Tropical depression two has formed offshore of the US east coast and is poised to become a tropical storm shortly. See area of interest #1 section below for Gulf of Mexico tropical development expected this week. See area of interest #2 section below for an eastern tropical Atlantic tropical wave of low pressure being monitored for development.


TROPICAL DEPRESSION TWO...The frontal low pressure offshore of North Carolina has quickly become the second tropical cyclone of the 2021 Atlantic Hurricane Season...tropical depression two. The depression is being steered quickly northeast by the upper trough and developing surface frontal low over eastern Canada...in alignment with the upper SW flow ahead of the upper trough. Despite this...the upper flow is still a little faster than the depression’s forward speed and thus the strongest thunderstorms have become displaced northeast of the center. However some renewed activity is bubbling very close to the center...thus the depression has a high chance of gaining tropical storm strength tonight. The divergence on the east side of the upper trough may be aiding this system’s thunderstorms...another meteorological positive for this system. The 24 hour forecast point is over cooler waters...thus I expect peak strength in the next 12 hours followed by weakening to 45 mph max sustained winds by 24 hours. By 48 hours...whatever is left of this system should be slingshotted into Newfoundland and absorbed into the larger aforementioned frontal low. Whatever rainfall and tangible weather Newfoundland experiences at that time would likely be attributed to the frontal low rather than this system.


This system will bring choppy seas to marine interests offshore of the northeast US and Atlantic Canada...with brief episodes of coastal sea swells and rip currents along the US New England coast as well as the Nova Scotia and Newfoundland coasts of Atlantic Canada.

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

0 Hr Position (1800Z Jun 14)...35 mph maximum sustained wind tropical depression centered at 35.5N-72W

IOH 24 Hr Forecast (1800Z Jun 15)...45 mph maximum sustained wind tropical storm centered at 40.5N-64W

IOH 48 Hr Forecast (1800Z Jun 16)...Absorbed by frontal low to the west while located over SE Newfoundland at 47.5N-55W


AREA OF INTEREST #1...The eastern Pacific tropical low pressure and Bay of Campeche tropical low pressure have merged into a broad tropical low pressure over SE Mexico. This feature and its ongoing widespread scattered thunderstorms remain supported by the outflow of upper ridging in the region. Computer models remain in strong agreement on the following:


(1) The current upper trough over eastern Canada will merge with upper vorticity that has been lingering over the southeastern US...resulting in a large upper trough dominating the eastern US. The western convergence zone of the large upper trough will continue to support surface ridging over the central US.


(2) Instead of having the central US surface ridge push the broad tropical low over SE Mexico westward...models instead 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 broad tropical low’s reformation northward in the Gulf of Mexico while transitioning into a subtropical or tropical cyclone boosted by the eastern divergence zone of the amplifying upper trough.


Forecast track in the outlook is an east and north track as this system transitions into a subtropical or tropical system supported by the aforementioned upper trough. I have raised long term odds of development to 80% due to the ongoing model consensus of an upper trough that becomes highly amplified which will keep shear low and upper divergence high in the Gulf of Mexico. By day 4...the upper trough is forecast to leave behind upper vorticity around the vicinity of the NW US Gulf coast. By day 5...the upper trough currently offshore of the western US will be passing over the Great Lakes region while potentially stretching the upper vorticity into a SW to NE elongation as it tries to grab the vorticity. Due to this elongation...westerly wind shear over this system could increase by day 5...thus I lower odds of development to 60% at that time...and also due to land interaction as this system nears the US Gulf coast.


Confidence is increasing for a coastal storm surge and wind event for the US Gulf coast anywhere from southeast Texas to Louisiana & Mississippi by Saturday. If the circulation of the forecast tropical or subtropical storm becomes large enough...it could drive coastal sea swells in the northeast Gulf (coastal Alabama and Florida panhandle). At this time...my forecast track tends to be east of the latest model consensus...more toward Louisiana and Mississippi...where the upper divergence maximum of the upper trough has been forecast to setup over the last few days (perhaps the more west solutions have a fragment of the amplifying upper trough cut-off into a vortex...with the vortex whirling this system more west)

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

IOH 24 Hr Outlook (1800Z Jun 15)...0% chance of tropical cyclone formation (eastern Tabasco/Chiapas border near 17.5N-92.5W)

IOH 48 Hr Outlook (1800Z Jun 16)...5% chance of tropical cyclone formation (west coast of Yucatan peninsula near 19N-90.5W)

IOH 72 Hr Outlook (1800Z Jun 17)...40% chance of tropical cyclone formation (Gulf of Mexico near 22.5N-90.5W)

IOH 96 Hr Outlook (1800Z Jun 18)...80% chance of tropical cyclone formation (Gulf of Mexico near 25N-90.5W)

IOH 120 Hr Outlook (1800Z Jun 19)...60% chance of tropical cyclone formation (coastal southeast Louisiana near 29N-90.5W)


AREA OF INTEREST #2...Atmospheric conditions in the eastern tropical Atlantic have become more conducive for development in recent days with a reduction in shear and increase in upper outflow while low-latitude upper vorticity in the region has weakened. Dry Saharan Air from Western Africa has so far precluded tropical development...however the tropical waves of low pressure that have recently emerged from Western Africa have also been impressive for June while producing strong and distinct thunderstorm fields. The most recent such wave to emerge from Africa has been the most impressive....with a tremendous area of thunderstorms last night that have spun up a low pressure currently located at 9N-22.5W. As time has progressed...thunderstorms have reduced while the low pressure spin ingests dry Saharan air. And given that climatologically June is usually early for tropical development in the eastern Atlantic...I am currently assigning 0% odds of development....especially given by the GFS is so far the only model showing development.

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

IOH 24 Hr Outlook (1800Z Jun 15)...0% chance of tropical cyclone formation (eastern tropical Atlantic near 9N-27.5W)


...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 tropical depression two...absorbed by eastern Canada frontal low at 42 hours while located 45N-59W

**For area of interest #1...possible weak tropical cyclone formation suggested near 23.5N-94W at 78 hours...after cyclonically looping in western Gulf of Mexico begins to drift north and reaches 25.5N-95.5W at 120 hours.

**For area of interest #2...no tropical cyclone formation shown


1200Z ECMWF Model Run...

**For tropical depression two...strengthens to a compact and strong tropical storm near 39N-65.5W at 24 hours...absorbed by eastern Canada frontal low at 48 hours while located just offshore of south-central Newfoundland

**For area of interest #1...tropical cyclone formation shown in the NW Gulf of Mexico near 27N-94W at 96 hours...makes landfall at the Texas/Louisiana border at 120 hours

**For area of interest #2...no tropical cyclone formation shown


1200Z GFS Model Run...

**For tropical depression two...strengthens to a compact tropical storm near 36N-70W at 12 hours...absorbed by eastern Canada frontal low at 51 hours while located on south coast of Newfoundland

**For area of interest #1...tropical cyclone formation shown in the Bay of Campeche near 19.5N-95W at 21 hours...moves SW into Veracruz by 42 hours while pivoting around a broader circulation to the SE...by 120 hours the broad circulation consolidates into a tropical cyclone moving toward the Louisiana coast.

**For area of interest #2...tropical cyclone formation suggested at 63 hours near 11N-35W...weakens to a surface trough near 16N-52.5W by 123 hours.


1200Z NAVGEM Model Run...

**For tropical depression two...strengthens to a tropical storm near 36.5N-70W at 18 hours...passes over SE Newfoundland at 54 hours as a non-tropical remnant low located along warm front of larger frontal low to the west...remnant low located at 54N-26W at 120 hours.

**For area of interest #1...tropical cyclone formation shown in eastern Bay of Campeche near 21N-93W at 78 hours....located offshore of the Texas coast at 120 hours

**For area of interest #2...no tropical cyclone formation shown

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