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 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #104

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


...THURSDAY AUGUST 27 2020 1:17 PM EDT...

See Hurricane Laura section below for the only currently active tropical cyclone in the Atlantic basin. See area of interest section below for eastern and central Atlantic tropical waves of low pressure being monitored for tropical cyclone formation.


Elsewhere...showers and thunderstorms in the central and western Caribbean Sea have been on the increase over the last couple of days due to the eastern divergence zone of a cut-off upper vortex retrograding westward through the region. Recently this upper vortex has weakened to an inverted upper trough as this cold core feature has been starved of cold air...and upper-level winds are becoming more favorable for tropical development in this region as the expansive upper ridge over the Gulf of Mexico and north Atlantic (with low shear and upper outflow) builds in the wake of the upper vorticity. Recently the NHC TAFB surface analysis has added a tropical wave of low pressure in this region...perhaps a wave that originated from Africa several days ago but was not well-defined till now...perhaps also playing a role in generating this thunderstorm activity. Any disturbance that develops here will track across the Yucatan peninsula of southeastern Mexico...then curve northward in the western Gulf of Mexico around the west side of a surface ridge to persist over the southeastern United States. None of the computer models develop this disturbance...but will consider adding this disturbance as an area of interest should it show signs of organization after crossing the Yucatan peninsula.


HURRICANE LAURA...Last afternoon and evening with Hurricane Laura continued to be impressive as the storm continued to take advantage of low shear and upper outflow beneath an expansive upper ridge that spans the Gulf of Mexico to north Atlantic...as well as rather warm 29 to 30 deg C Gulf of Mexico waters...continuously intensifying to a high end category 4 hurricane with 150 mph maximum sustained winds and 937 mb central pressure in the hours before landfall. Laura essentially made landfall at this peak intensity just east of the Texas/Louisiana border in the Cameron area in the early morning hours. I previously speculated that southwesterly upper winds over far east Texas driven by a central United States cut-off upper trough would prevent category 5 intensity at landfall while working against Laura's western outflow...and this is what appears to have occurred. However these upper winds were not able to weaken Laura from its peak intensity during landfall I think for two reasons...one is the hurricane tracked a little further east which increased the distance between the core of Laura and the upper westerly winds to the west...and second the tremendous latent heat release of the hurricane's thunderstorms may have weakened the central United States cold core upper trough and its upper westerly winds.


Because Laura is currently northeast of my previous forecast track...I have adjusted my forecast track points northeastward accordingly. After 24 hours...the central United States upper trough currently drawing Laura northward across Louisiana and toward Arkansas will be pushed eastward by another upper trough incoming from western Canada...which should quickly curve Laura more eastward in track toward the Kentucky/southern Ohio valley/Appalachian mountain region. There remains a split in the modeling regarding the fate of what will be Laura's inland remnant low pressure....with one camp dissipating Laura's remnant while it gets caught in the western convergence zone of the upper trough from western Canada...the second camp showing Laura's remnant low surviving as a non-tropical frontal low pressure that moves into the northwest Atlantic...possibly close to or over the coast of the northeastern United States and southeast Canada...while supported by the divergence on the east side of the upper trough. I lean toward the second camp as Laura is further east and thus will more likely engage with the divergent east side of the incoming upper trough to dive in from western Canada. However in the second camp some modeling shows Laura losing its identity to another frontal cyclone to form from the same upper trough and just to the north...while models like the 0600Z NAVGEM run show Laura's remnant becoming the dominant frontal cyclone.


Regarding strength...Laura is below my previous forecast as the early eastward turn yesterday night in Laura's track moved the hurricane ashore a little sooner than I previously forecasted. As of 11 AM EDT (10 AM CDT) Laura was barely a category 1 hurricane...and soon will weaken to a tropical storm and then tropical depression while moving out of Louisiana and into Arkansas later today. See bulletins at the home page of this site for an update on Laura's impact potential given this current outlook.

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

0 Hr Position (1200Z Aug 27)...85 mph maximum sustained wind hurricane centered over west-central Louisiana at 31.7N-93.1W

IOH 24 Hr Forecast (1200Z Aug 28)...30 mph maximum sustained wind tropical depression centered over the eastern Arkansas/Missouri border at 36.2N-90.2W

IOI 48 Hr Forecast (1200Z Aug 29)...Remnant low pressure centered over the Virginia/West Virginia Border at 37.5N-80W


AREA OF INTEREST #1...A tropical wave of low pressure is entering the central tropical Atlantic from the eastern tropical Atlantic...and thunderstorm activity associated with this disturbance has increased near a rotation in the vicnity of 11N-40W and to the southwest. To the west-northwest of the tropical wave...a large swath of dry saharan air looms. Outside of the dry air...conditions in the tropical Atlantic are favorable for this tropical wave to develop as a tropical upper ridge axis with low shear and upper outflow will prevail in the region. However my peak 5-day odds of tropical cyclone formation are only 20% at the present time as dry saharan air has recently had a history of hampering development in the tropical Atlantic to the east of the Lesser Antilles. These odds however are raised from my previous outlook as the thunderstorm activity associated with this wave has increased compared to 24 hours ago. Upper vorticity that lies to the northwest is not expected to hamper this wave's development as it quickly retrogrades westward out of the way under the influence of expanding north Atlantic upper ridging. On a final note...multiple models shows the strong tropical wave to the east...currently offshore of western Africa and recently introduced into the National Hurricane Center tropical weather outlook...catching up to this wave and gradually merging with it...see area of interest #2 section below for more on the wave to the east. However given that this wave is currently the better organized of the two...I prefer to assume this wave will be the dominant. I have begun to mention potential effects of this tropical wave to the Lesser Antilles on the home page bulletins of this site as this wave is about 3 to 4 days away from reaching those islands.

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

IOH 24 Hr Outlook (1200Z Aug 27)...5% chance of tropical cyclone formation (tropical Atlantic near 11N-45W)

IOH 48 Hr Outlook (1200Z Aug 28)...10% chance of tropical cyclone formation (tropical Atlantic near 11.5N-50W)

IOH 72 Hr Oulook (1200Z Aug 29)...15% chance of tropical cyclone formation (tropical Atlantic east of the Lesser Antilles near 12N-55W)

IOH 96 Hr Outlook (1200Z Aug 30)...20% chance of tropical cyclone formation (just east of the southern Lesser Antilles near 12.5N-60W)

IOH 120 Hr Outlook (1200Z Aug 31)...20% chance of tropical cyclone formation (eastern Caribbean Sea near 13N-65W)


AREA OF INTEREST #2...A tropical wave of low pressure that has recently exited the west African coast is producing curved bands of thunderstorms...suggesting that the lowest pressure is in the vicinity of 15N-19W. Computer models generally show this wave move rapidly westward across the Atlantic tropics and catch up to the wave mentioned in area of interest #1. The 5-day graphical National Hurricane Center tropical weather outlook seems to agree with this idea while showing the wave already reaching the Lesser Antilles by day 5. Other than dry saharan air blanketing much of the Atlantic tropics...conditions will be favorable for development as a tropical upper ridge axis with low shear and upper outflow will prevail in the region. However I only have peak 5-day odds of development at a rather low 10% as the lowest pressure of this tropical wave so far appears to be further north toward 15N latitude...a position that makes the wave more vulnerable to ingesting the dry saharan air...and also the vorticity of the tropical wave in area of interest #1 may keep this tropical wave pushed further north toward the dry saharan air. I drop the odds of development back to 0% by the end of the 5-day forecast period while assuming the better organized tropical wave in area of interest #1 becomes the dominant while this wave catches up to and merges with it. On a final note...some of the currently central Atlantic upper vorticity will become at first pushed toward the far eastern Atlantic by the expanding north Atlantic upper ridge...and then this upper ridge will push this upper vorticity southwestward on a path chasing this tropical wave by the end of the forecast period. However with the fast westward pace of this tropical wave...I do not expect the upper vortex to catch up to this wave and affect it.

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

IOH 24 Hr Outlook (1200Z Aug 27)...0% chance of tropical cyclone formation (west of the southern Republic of Cabo Verde Islands near 15N-27W)

IOH 48 Hr Outlook (1200Z Aug 28)...5% chance of tropical cyclone formation (tropical Atlantic near 15N-35W)

IOH 72 Hr Oulook (1200Z Aug 29)...10% chance of tropical cyclone formation (tropical Atlantic near 15N-43W)

IOH 96 Hr Outlook (1200Z Aug 30)...0% chance of tropical cyclone formation (tropical Atlantic near 15N-51W)

IOH 120 Hr Outlook (1200Z Aug 31)...0% chance of tropical cyclone formation (tropical Atlantic just east of the Lesser Antilles near 15N-59W)


...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 Hurricane Laura...remnant low pressure reaches the Arkansas/Missouri border in 36 hours...dissipates by 42 hours. For area of interest #1...organizes into a troipcal low pressure in the central Caribbean Sea in the long range (156 hours). For area of interest #2...no tropical cyclone formation shown while gradually merging with area of interest #1 in the long range.


0000Z ECMWF Model Run...For Hurricane Laura...remnant low pressure reaches the Arkansas/Missouri/Tennesse/Kentucky/Illionis border region in 48 hours...the North Carolina/Virginia border in 72 hours...gradually loses identity to much larger frontal cyclone developing to the north after it moves into the northwest Atlantic after 72 hours.. For areas of interest #1 and #2...no tropical cyclone formation shown.


0600Z GFS Model Run...For Hurricane Laura...remnant low pressure reaches the Arkansas/Missouri/Tennesse/Kentucky/Illionis border region in 36 hours...dissipates over Kenutcky in 48 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...no tropical cyclone formation shown while gradually merging with area of interest #1 in the long range.


0600Z NAVGEM Model Run... For Hurricane Laura...remnant low pressure reaches the Arkansas/Missouri/Tennesse/Kentucky/Illionis border region in 36 hours...reaches the southeast coast of New Jersey in 66 hours...remnant low pressure begins to re-intensify as a non-tropical frontal cyclone and moves into Newfoundland in 90 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...gradually merges with area of interest #1 in the long range...organizes into a tropical low pressure over the south coast of eastern Cuba in 156 hours.

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