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 #105

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


...FRIDAY AUGUST 28 2020 3:00 PM EDT...

See remnants of Laura section below for a final statement on this system. See area of interest sections below for eastern and central Atlantic tropical waves of low pressure being monitored for tropical cyclone formation. Elsewhere...the tropical wave of low pressure in the western Caribbean Sea has made landfall across southeastern Mexico and is already emerging into the Bay of Campeche in the southwestern Gulf of Mexico. However this system has lost thunderstorm activity and tropical development here is therefore not likely.


REMNANTS OF LAURA...Over the last 24 hours Hurricane Laura decayed to an inland tropical storm and then tropical depression over Arkansas. The remnant low pressure is now being supported by the eastern divergence zone of a cold core central United States upper trough that has also been weakening while starved of cold air. Laura is turning eastward toward Kentucky and Tennessee while the central United States upper trough is beginning to shift east while kicked by a shortwave upper trough from western Canada. Models now agree that the two upper troughs will merge...with the maximum divergence on the east side of the combined trough being further north such that a new frontal cyclone develops while Laura loses its identity in the south side of the frontal cyclone in the next 24 hours. Heavy rainfall with some flooding potential directly associated with Laura's remnant low pressure will spread into Kentucky and Tennessee today...with the moisture from Laura becoming spread across the northeastern United States by the frontal cyclone to develop to the north by tomorrow and onwards. This is my final statement on Laura on this blog as it is no longer a tropical cyclone.


AREA OF INTEREST #1...The tropical wave of low pressure currently in the central tropical Atlantic is producing broad cyclonic turning with showers and thunderstorms in the vicinity of 12.5N-46W. Meanwhile another large tropical wave of low pressure to the east (area of interest #2) is becoming stretched northwest-to-southeast as the northern part of the wave appears to be in stronger easterly trade winds on the south side of the Atlantic subtropical ridge while the south side of the trpoical wave appears to be gravitated toward the low pressure field of the next tropical wave that will be emerging from western Africa. The northwest part of that tropical wave is well-defined by a broad cloud swirl near 19N-35W and circular flare up of thunderstorms near 12.5N-35W. Over the next 24 hours and in accordance with some of the latest model runs...I forecast the westward speed of the tropical wave associated with this area of interest to slow to about 3W longitude per day while it merges with the tropical wave fragment at 35W racing toward this system...with the low pressure field of the incoming tropical wave fragment responsible for slowing the westward progress of this wave. After that time...I forecast the merged system to then re-start a typical 5W longitude per day progression across the Atlantic tropical belt. By 72+ hours...I slightly bend the track of this system northward while it reaches the weaker western extent of the Atlantic surface subtropical ridge...to be kept generally weaker by a pair of frontal cyclones to develop and pass over the northeastern United States and Canada during the 120 hour forecast period. I have dropped short term odds of development to 0% to give time for this tropical wave to merge with the incoming tropical wave fragment and consolidate after the merger. I keep long term odds of development at a low 20% and toward 120 hours as only the CMC and NAVGEM suggest this system develops as it moves into the central Caribbean Sea by that timeframe. Regarding upper-level winds...the streteched upper vorticity from the Caribbean Sea to central and northeast Atlantic is expected to consolidate into two lobes of upper vorticity that retrograde westward around high-latitude upper ridging to be induced by the warm sectors of the frontal cyclones that develop over Canada...with this disturbance forecast to be in a favorable low shear and upper outflow environment between both lobes of upper vorticity. Thus the only negative factors that prevent development would be the structure of this disturbance...especially if it remains disorganized while merging with the incoming tropical wave fragment...and maybe some dry saharan air layer intrusions. I have continued to mention potenial effects of this tropical wave to the Lesser Antilles on the home page bulletins of this site as this wave is about 2 to 3 days away from reaching those islands.

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

IOH 24 Hr Outlook (1200Z Aug 28)...0% chance of tropical cyclone formation (tropical Atlantic near 12.5N-49W)

IOH 48 Hr Oulook (1200Z Aug 29)...0% chance of tropical cyclone formation (tropical Atlantic east of the Lesser Antilles near 12.5N-54W)

IOH 72 Hr Outlook (1200Z Aug 30)...10% chance of tropical cyclone formation (just east of the southern Lesser Antilles near 12.5N-59W)

IOH 96 Hr Outlook (1200Z Aug 31)...15% chance of tropical cyclone formation (eastern Caribbean Sea near 13N-64W)

IOH 120 Hr Outlook (1200Z Sep 1)...20% chance of tropical cyclone formation (central Caribbean Sea near 13.5N-69W)


AREA OF INTEREST #2...The tropical wave of low pressure in the eastern Atlantic has become streteched northwest to southeast as the northern part of the wave appears to be in stronger easterly trade winds on the south side of the Atlantic subtropical ridge while the south side of the trpoical wave appears to be gravitated toward the low pressure field of the next tropical wave that will be emerging from western Africa. The National Hurricane Center tropical weather outlook agrees with this assessment...and have zoned in on the southeastern part of the tropiacl wave in the vicinity of 12.5N-24W as the part of the wave to watch for development in the coming days. It is remarkable to note that the CMC...NAVGEM...GFS...and ECMWF agree that this part of the tropical wave will become generally stationary southwest of the Republic of Cabo Verde Islands while merging with the next wave to exit western Africa...and all models also agree today on developing the merged system. There is just disagreement from model to model as to exactly when the merged system will start moving westward around the Atlantic subtropical ridge. For now my vote in the outlook below is that it will take about 48 hours for the two tropical waves to merge...after which time I gradually ramp up the westward speed of the merged wave to a typical 5W per day longitude progression around the Alantic subtropical ridge and by 120 hours. It is also after 48 hours when I start ramping up the odds of development above 0% as this is when the above-mentioned models start suggesting some development (CMC suggests development already by 72 hours...the others suggest development later on). My peak 120-hour odds of development are at a higher 30% compared to area of interest #1 as the models are in stronger agreement on developing this system unlike area of interest #1. However I am at only 30% as I am uncertain if the merged tropical wave will remain disorganized or not during the forecast period.

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

IOH 24 Hr Outlook (1200Z Aug 28)...0% chance of tropical cyclone formation (southwest of the Republic of Cabo Verde Islands near 12.5N-25W)

IOH 48 Hr Outlook (1200Z Aug 29)...0% chance of tropical cyclone formation (southwest of the Republic of Cabo Verde Islands near 12.5N-26W)

IOH 72 Hr Oulook (1200Z Aug 30)...10% chance of tropical cyclone formation (tropical Atlantic near 12.5N-29W)

IOH 96 Hr Outlook (1200Z Aug 31)...20% chance of tropical cyclone formation (tropical Atlantic near 12.5N-34W)

IOH 120 Hr Outlook (1200Z Sep 1)...30% chance of tropical cyclone formation (tropical Atlantic near 12.5N-39W)


...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 remnants of Laura...surface low pressure dissipates over the Kentucky/West Virginia border in 24 hours. For area of interest #1...organizes into a troipcal low pressure in the central Caribbean Sea east of Nicaragua in the long range (138 hours). For area of interest #2...northwest part of tropical wave merges with area of interest #1 without tropical cyclone formation...southeast part of tropical wave nearly stationary southwest of the Republic of Cabo Verde Islands for the next 48 hours while possibly merging with another tropical wave to emerge from western Africa...tropical cyclone formation suggested near 12.5N-30W in 72 hours.


0000Z ECMWF Model Run...For remnants of Laura...loses identity over western Kentucky by 24 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...northwest part of tropical wave merges with area of interest #1 without tropical cyclone formation...southeast part of tropical wave nearly stationary southwest of the Republic of Cabo Verde Islands while possibly merging with another tropical wave to emerge from western Africa...tropical cyclone formation suggested near 13N-36W in 168 hours.


1200Z GFS Model Run...For remnants of Laura..dissipates over Kentucky/West Virginia border at 24 hours. For area of interest #1...no tropical cyclone formation shown. For area of interest #2...northwest part of tropical wave merges with area of interest #1 without tropical cyclone formation...southeast part of tropical wave nearly stationary southwest of the Republic of Cabo Verde Islands while possibly merging with another tropical wave to emerge from western Africa...tropical cyclone formation suggested near 13N-28.5W in 120 hours.


0600Z NAVGEM Model Run... For remnants of Laura....dissipates over Kentucky/West Virginia border at 24 hours. For area of interest #1...organizes into a tropical low pressure in the Caribbean Sea centered just east of the Nicaragua/Honduras border in 132 hours. For area of interest #2...northwest part of tropical wave merges with area of interest #1 without tropical cyclone formation...southeast part of tropical wave nearly stationary southwest of the Republic of Cabo Verde Islands while possibly merging with another tropical wave to emerge from western Africa...organizes into a tropical low pressure in 90 hours that cyclonically loops over the Republic of Cabo Verde Islands after that time while possible tropical cyclone formation suggested.

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