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 #21

*******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 15 2021 12:46 PM EDT...

The Atlantic tropics remain unusually busy for mid-June. Tropical Storm Bill is currently racing northeastward offshore of Atlantic Canada. 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. See area of interest #3 section below for notes on the current area of disturbed weather offshore of the southeastern United States...which could evolve into a subtropical cyclone north of Bermuda on Friday.


TROPICAL STORM BILL...Bill has exceeded intensity expectations while reaching 60 mph maximum sustained winds (the NHC yesterday forecasted a peak of 50 mph...and I had forecasted yesterday that Bill would be weakening from peak intensity instead of reaching it now). This has happened despite Bill reaching waters temps below 26 deg C and losing thunderstorm intensity. It could be the winds on the southeast side of Bill have been accelerated by the fast forward motion of the tropical storm...and Bill is also below the supportive divergence zone of an incoming upper trough over the eastern US/Canada. Thus some of its recent gain in strength is explained by non-tropical processes. Models agree on Bill losing its tropical characteristics and identity while hurtled northeastward into southeastern Nefoundland in the next 24 hours by the large frontal low developing over eastern Canada...and my forecast below shows this. My forecast track is shifted eastward given Bill's current position. On the home page bulletins of this site...I have added the possiblity of Bill driving some gusty winds over southeastern Newfoundland given that Bill is a little stronger than forecast and could retain its identity long enough for a landfall.

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

0 Hr Position (1200Z Jun 15)...60 mph maximum sustained wind tropical storm centered at 40.5N-62W

IOH 24 Hr Forecast (1200Z Jun 16)...Absorbed by frontal low to the west while located over SE Newfoundland at 47.5N-53.5W


AREA OF INTEREST #1...The broad tropical low pressure centered over southeastern Mexico has become better defined this morning with outer thick bands of thunderstorms. This feature remains supported by the outflow of upper ridging in the region. Recently the upper vorticity that was lingering over the southeastern US has merged with an upper trough that had been over eastern Canada...resulting in a large upper trough over the eastern US. The western convergence zone of this upper trough is continuing to support surface ridging over the central US. The upper trough is already amplifying southward into the western Gulf of Mexico due to amplification of adjacent western US warm upper ridging (associated with the current western North America frontal system's warm sector). Therefore instead of the central US surface ridging keep the broad tropical low pressure trapped over southeastern Mexico or pushing it westward...the broad tropical low pressure is instead expected to relocate northeastward into the Gulf of Mexico while transitioning into a subtropical or tropical cyclone boosted by the eastern divergence zone of the amplifying upper trough. Due to continued agreement in the models for the formation of a subtropical or tropical cyclone in the Gulf of Mexico over the next few days (due to how amplified the upper trough will become in the western Gulf of Mexico...which will keep shear low and upper divergence high)...I have begun a tropical cyclone formation forecast below...providing specific track and intensity forecast points.


At this time...my forecast track leans 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. So I have nudged my updated forecast track westward as we are not that far out from this event beginning and some model runs are keeping a westward solution towards the southwest Louisiana/Texas coastal region. Due to the size of the upper divergence zone on the east side of the upper trough...expecting a large/broad tropical cyclone with a lax surface pressure gradient...and in addition to the upper trough potentially limiting thunderstorms on the west side of the center...I only forecast a peak of 50 mph maximum sustained winds at the present time. By day 3...the upper trough is forecast to leave behind upper vorticity around the NW US Gulf coast region. By day 4...the upper trough currently moving into 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 4...thus I forecast some weakening as this system makes landfall. By day 5 and beyond...this system could transition into a gusty non-tropical frontal cylcone that moves across the southeastern and east-central US...as an upper trough currently over the north Pacific ends up potentially merging with the NW US Gulf coast vorticity into an amplified upper trough that supports the surface remnants of this system. It is also possible the two upper features don't merge and the surface remnants of this system dissipates quickly after landfall. Models have been depicting both scenarios with equal weight...and given that one of the players is currently far way in the north Pacific it is hard to know if this system will become an impactful remnant frontal cyclone over the inland US at this time.


Confidence is increasing on a Saturday coastal storm surge and wind event anywhere from coastal southeast Texas to Louisiana & Mississippi. Gather storm preparation supplies early to avoid last minute crowding...espeically for those not yet vaccinated against the COVID-19 virus. Unvaccianated people who live in an area prone to coastal storm surge in this region whould also come up with a plan to relocate to a hotel or family/friend residence further inland...as a public storm shelter may not be as ideal for controlling your exposure to COVID-19. The circulation of this system is expected to be large in size...therefore this system could bring coastal sea swells to the Alabama and Florida panhandle coast as well this weekend.

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

0 Hr Position (1200Z Jun 15)...Broad tropical low pressure centered over the eastern Tabasco/Chiapas border at 17.5N-92.5W

IOH 24 Hr Forecast (1200Z Jun 16)...Broad tropical low pressure centered over the west coast of Yucatan peninsula at 19N-90.5W

IOH 48 Hr Forecast (1200Z Jun 17)...35 mph maximum sustained wind tropical depression centered over the Gulf of Mexico at 22.5N-91W

IOH 72 Hr Forecast (1200Z Jun 18)...50 mph maximum sustained wind tropical storm centered over the Gulf of Mexico at 26N-91W

IOH 96 Hr Forecast (1200Z Jun 19)...45 mph maximum sustained wind tropical storm centered over southeastern Louisiana at 30N-91W

IOH 120 Hr Forecast (1200Z Jun 20)...Remnant frontal low centered over the southern Mississippi/Alabama border at 31.2N-88.5W


AREA OF INTEREST #2...The vigorous tropical wave of low pressure in the eastern tropical Atlantic continues to lack thunderstorms while ingesting dry saharan air. This goes to show you that despite having a well-defind spin...and despite being over favorable warm waters...low shear...and upper outflow beneath upper ridging in the region that dry air can hamper development. The GFS model has dropped showing development of this wave...and climatology shows that development in this part of the Atlantic is difficult in June. Therefore I maintain 0% odds of tropical development. I plan this to be my final statement on this area of interest unless the NHC continues to mention it in their tropical weather outlook.

******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-31W)


AREA OF INTEREST #3...In the wake of Tropical Storm Bill...somewhat organized thunderstorm bands have developed offshore of the southeastern US with the support of upper divergence out ahead of the currently amplifying upper trough over the eastern US. In response to amplifying upper ridging over the western US (associated with the current western North America frontal system's warm sector)...the upper trough over the eastern US is forecast to amplify further into two possible vortices...one over the open western Atlantic to the north of Bermuda...and another over the northwestern US Gulf coast region to be entangled with area of interest #1. The increasing divergence zone of the amplifying upper vorticity that enters and crosses the western Atlantic may cause the activity currently offshore of the southeast US to evolve into a surface low pressure that shifts east to the waters north of Bermuda...and moreover the surface low could briefly acquire tropical characteristics on Friday despite moving east past the warm Gulf stream and into slightly cooler 24 deg C waters. However I only have low 15% odds of subtropical cyclone development at the present time as the temperatures of the upper vorticity may not be quiet cold enough for the development of instability and thunderstorms (the 200 mb height of the vorticity is forecast to be 1209 dekameters on Friday...would like to see 1200 dekameters or less for more confidence in subtropical or tropical development). However what may offset the slightly cooler water and slightly too warm upper vorticity is the amount of upper divergence forecast to occur on the east side of the upper vorticity which could allow for thunderstorm generation anyway. I also have low odds of development as models are mixed on how organized the upper vorticity and resulting surface low may be (for example in the sample of runs captured in the model summary below...the GFS is the most organized and the CMC and NAVGEM are showing a less organized system).


I drop odds of development back down to 0% by Saturday (96 hours) as the upper vorticity warms while remaining cut-off from high latitude cold air...which will make thermodynamic conditions less favorable for thunderstorms.

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

IOH 24 Hr Outlook (1200Z Jun 15)...0% chance of subtropical cyclone formation (southeast of Cape Hatteras North Carolina near 34N-74W)

IOH 48 Hr Outlook (1200Z Jun 16)...0% chance of subtropical cyclone formation (western Atlantic near 34N-70W)

IOH 72 Hr Outlook (1200Z Jun 17)...15% chance of subtropical cyclone formation (north of Bermuda near 35N-65W)

IOH 96 Hr Outlook (1200Z Jun 18)...0% chance of subtropical cyclone formation (western Atlantic near 37.5N-62W)


...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)


0000Z CMC Model Run...

**For Tropical Storm Bill...absorbed by eastern Canada frontal low at 30 hours while located just offshore of SE Nova Scotia

**For area of interest #1...possible weak tropical cyclone formation suggested near 23N-96.5W at 84 hours...after cyclonically looping in western Gulf of Mexico begins to drift north and makes landfall just south of Matagorda Bay Texas at 108 hours.

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

**For area of interest #3...weak surface low becomes defined west of Bermuda near 32.5N-68.5W at 78 hours...accelerates northeast toward SE Newfoundland by 126 hours.


0000Z ECMWF Model Run...Not available at above-mentioned source


0600Z GFS Model Run...

**For Tropical Storm Bill...absorbed by eastern Canada frontal low at 33 hours while making landfall on the south coast of Newfoundland

**For area of interest #1...tropical cyclone formation shown near 23N-92.5W at 66 hours...makes landfall over southwest Louisiana at 102 hours

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

**For area of interest #3...surface low forms offshore of Cape Fear North Carolina at 30 hours...possible subtropical development suggested north-northwest of Bermuda near 35.5N-66W at 78 hours...while south of Newfoundland at 126 hours becomes abosrbed by frontal low quickly passing north of the Great Lakes region over eastern Canada


0600Z NAVGEM Model Run...

**For Tropical Storm Bill...loses identity at 36 hours to the larger frontal low to the west just after making landfall over Newfoundland

**For area of interest #1...tropical cyclone formation shown in the Bay of Campeche near 20.5N-94W at 60 hours....makes landfall between Matagorda Bay and Galveston Bay Texas at 114 hours as a strong tropical storm.

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

**For area of interest #3...an elongated surface trough becomes defined northwest of Bermuda at 72 hours...trough strengthens into a large surface low near 35.5N-61.5W at 90 hours...while south of Newfoundland at 126 hours becomes abosrbed by frontal low quickly passing north of the Great Lakes region over eastern Canada

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