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 #71

*******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 5 2021 6:55 PM EDT...

See the area of interest sections below for multiple areas being monitored for tropical development in the Atlantic...which include:

(1) area of interest #1...tropical wave of low pressure that has recently entered the eastern tropical Atlantic...heavy rains could reach the Republic of Cabo Verde Islands by tomorrow regardless of further development or not.

(2) area of interest #2...large central tropical Atlantic wave of low pressure...the wave could cross the Lesser Antilles in about 5 days.


AREA OF INTEREST #1...The vigorous tropical wave of low pressure that was over western Africa has made its way into the far eastern tropical Atlantic. The wave's center of spin appears to be currently located at 11.5N-17.5W...with thunderstorm activity south of the center and a recent new burst of strong thunderstorms west of the center. Meanwhile activity on the north side of the wave is limited by dry saharan air. Located nearby to the west...and also west of the Republic of Cabo Verde Islands...is the remnant low pressure of what was Invest 91-L (what was area of interest #1 in my birdseye view post yesterday). The GFS and NAVGEM have shown this tropical wave and 91-L undergoing a fujiwhara type interaction which would cuase this wave to initially have a more north track. Given that 91-L had a distinct presence earlier today with a burst of thunderstorms...I have to agree that 91-L will have some influence on this wave's track and have increased the northward angle in my forecast track in my updated outlook below. However I do not agree with 91-L becoming the dominant circulation as it has recently lost its thunderstorm burst..therefore I bend the forecast track more westward after 48 hours which is around the time this wave would absorb 91-L. By 120 hours I bend the track a little more northward as there is potential for this wave to be influenced by the current upper vortex in the eastern Atlantic which is forecast to slowly retrograde southwest ahead of the tropical wave.


I have raised my odds of development to 50% by day 5 due to the ongoing thunderstorm activity associated with the wave. However this is still not as high as the NHC outlook which has 70% odds by day 5 as of this writing...because I see that this wave could still have challenges in organizing while absorbing 91-L and as the possible fujwhara interaction with 91-L could push this wave more north toward the dry saharan air and cooler waters north of 15N latitude in the far east Atlantic. This is also why I do not rapidly ramp up the odds of development to 50%...instead waiting till day 5 to do so when the wave's forecast track moves it into a more vast area of warm 26+ deg C water. Regardless of further development or not...this wave could bring heavy rains to the Republic of Cabo Verde Islands by tomorrow.

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

IOH 24 Hr Outlook (1800Z Aug 6)...10% chance of tropical cyclone formation (southeast of the Republic of Cabo Verde Islands near 12.5N-22.5W)

IOH 48 Hr Outlook (1800Z Aug 7)...30% chance of tropical cyclone formation (just southwest of the Republic of Cabo Verde Islands near 14N-27W)

IOH 72 Hr Outlook (1800Z Aug 8)...35% chance of tropical cyclone formation (eastern tropical Atlantic near 14.5N-31W)

IOH 96 Hr Outlook (1800Z Aug 9)...40% chance of tropical cyclone formation (eastern tropical Atlantic near 15N-35W)

IOH 120 Hr Outlook (1800Z Aug 10)...50% chance of tropical cyclone formation (eastern tropical Atlantic near 16N-39W)


AREA OF INTEREST #2...The rather large tropical wave of low pressure that has been moving through the central tropical Atlantic currently has its axis at 50W longitude which has had a broad rotation but a lack of thunderstorms perhaps from its ingestion of dry saharan air. However more interesting activity is occuring on the east side of the wave toward 12.5N-40W where an organizing low pressure spin with thunderstorm banding features is developing. The 12Z ECMWF and NAVGEM picked up on this feature and develops it into a bonafide tropical cyclone. The 12Z CMC and GFS have also picked up on this feature but are not excited about developing it. The track forecasting for this feature is also quiet varied...with the CMC and NAVGEM showing this feature moving west-northwest while undergoing a fujiwhara interaction with the remainder of the wave and reaching the waters near the northern Lesser Antilles by day 5. The GFS and ECMWF shows such a strong fujiwhara interaction in the short-term with the remnants of Invest 91-L and area of interest #1 to the east such that the feature initially drifts south...followed by a west track with little northward angle as the initial fujiwhara interaction causes seperation of the feature from the rest of the wave such that it can no longer couple with the remainder of the wave and bend north. Because recent satellite loops show a southward drift with the new low pressure feature...my forecast in the updated outlook below shows an initial southwest track. Because its hard to know if the GFS/ECMWF or NAVGEM/CMC track will verify...I compromise between these two ideas...releasing this feature from the tug of 91-L sooner than the GFS/ECMWF show and thus allowing some northward angle in track to ensue in the longer range as the low pressure feature couples with and orbits around the east side of the wave.


I have raised my odds of development for this area of interest to 50% by day 5 due to the development of the eastern low pressure feature...which is higher than the NHC's outlook of 20% by day 5. I also justify the higher odds as the upper-level environment of tropical upper ridging (low shear and upper outflow) is forecast to persist and could be helpful in development. While I do not instantaneously raise the odds to 50% due to the thunderstorms in the low pressure feature being more moderate rather than strong on colorized infrared satellite...I do ramp the odds up a little faster than I did with area of interest #1 as this system will not have to contend with as much dry saharan air and as its forecast track over the next five days is over waters warmer than area of interest #1. Interests in the Lesser Antilles should monitor the progress of the tropical wave due to its recent development of the low pressure feature.

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

IOH 24 Hr Outlook (1800Z Aug 6)...10% chance of tropical cyclone formation (central tropical Atlantic near 11N-42W)

IOH 48 Hr Outlook (1800Z Aug 7)...30% chance of tropical cyclone formation (central tropical Atlantic near 11.5N-46W)

IOH 72 Hr Outlook (1800Z Aug 8)...40% chance of tropical cyclone formation (central tropical Atlantic near 13.5N-51W)

IOH 96 Hr Outlook (1800Z Aug 9)...50% chance of tropical cyclone formation (east of the Lesser Antilles near 15.5N-56W)

IOH 120 Hr Outlook (1800Z Aug 10)...50% chance of tropical cyclone formation (just east of the northern Lesser Antilles near 17.5N-60W)


...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 area of interest #1...tropical wave of interest develops a low pressure spin near 12.5N-21W at 30 hours...center of spin reaches 15N-36W by 120 hours.

**For area of interest #2...east end of the large and broad tropical wave develops a low pressure spin near 13.5N-38W at 30 hours...the low pressure spin weakens to a trough near 15N-42.5W at 66 hours...surface trough turns west and reaches the waters northeast of the Lesser Antilles by 120 hours while retaining a sharp definition.


1200Z ECMWF Model Run...

**For area of interest #1...tropical wave of interest develops a broad low pressure spin located just south of the Republic of Cabo Verde Islands by 48 hours...wave loses low pressure spin while crossing 28W longitude by 72 hours.

**For area of interest #2...east end of the large and broad tropical wave develops a low pressure spin near 13.5N-39W at 24 hours...low pressure spin remains generally stationary through 72 hours while tugged by area of interest #1 to the east...low pressure spin begins to move west by 96 hours and becomes a tropical depression near 12N-40W...tropical depression strenghtens into a stronger tropical cyclone by 120 hours while located at 14N-41.5W.


1200Z GFS Model Run...

**For area of interest #1...tropical wave of interest develops a low pressure spin located near 11.5N-20W at 24 hours...while the low pressure spin gradually strengthens through 48 hours at a location south of the Republic of Cabo Verde Islands it begins to compete with surface low to the west associated with what was Invest 91L...at 102 hours the two circulations merge while located near 16N-32W...the merged circulation reaches 17.5N-33W at 120 hours.

**For area of interest #2...east end of the large and broad tropical wave develops a low pressure spin near 13.5N-38W at 39 hours...the remnants of Invest 91L and area of interest #1 to the east push this circulation southward through 90 hours...surface low turns west and reaches 11.5N-44.5W at 120 hours.


1200Z NAVGEM Model Run...

**For area of interest #1...tropical wave of interest develops a low pressure spin located near 12N-20W at 30 hours...the low pressure spin weakens while undergoing competition with what was Invest 91L...the remnants of 91L pushes the weakening low pressure spin into the Republic of Cabo Verde Islands by 78 hours...low pressure spin dissipates by 84 hours while the remnants of 91L become dominant near 11N-32W...the remnants of this area of interest through a fujiwhara interaction pulls the remnants of 91L northward into 16N-30W by 120 hours.

**For area of interest #2...east end of the large and broad tropical wave develops a low pressure spin near 12.5N-44W at 12 hours...while gradually developing into a tropical cyclone the low pressure spin moves west-northwest around the remainder of the wave to the west and reaches 17.5N-56.2W by 120 hours.

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