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 #70

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

...WEDNESDAY AUGUST 4 2021 11:00 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...surface trough of low pressure in the vicinity of the Republic of Cabo Verde Islands…recently cancelled as an area of interest

(2) area of interest #2...surface low pressure area along a frontal boundary along the eastern United States coast…being cancelled as an area of interest but could still bring heavy rains to the northeast United States coast over the next day or so.

(3) area of interest #3...tropical wave of low pressure currently over western Africa which has model support showing development when it enters the eastern tropical Atlantic in a few days…heavy rains could reach the Republic of Cabo Verde Islands by Friday regardless of further development or not.

(4) area of interest #4…large central tropical Atlantic wave of low pressure which helped to spawn area of interest #1 days ago…the wave could cross the Lesser Antilles in 4 to 5 days.


AREA OF INTEREST #1...The National Hurricane Center (NHC) in their tropical weather outlook continues to mention the surface trough of low pressure currently over the Republic of Cabo Verde Islands. In the NHC TAFB surface analysis...the surface trough has been upgraded to a seperate tropical wave...but is interesting to note that this feature was spawned by the much larger tropical wave of low pressure now associated with area of interest #4 and even kicked northward into the islands by the east side of the larger wave. Because of the dry Saharan air layer in progress over and north of the islands...the surface trough has been absent of thunderstorm activity over the last several hours...so even though the NHC continues to mention the surface trough in their outlook they also have odds of development at 0%. I agree with 0% development odds as the surface trough begins to shift west under the influence of the Atlantic surface ridge. I plan this to be my final statement on this area of interest on this blog unless it continues to be mentioned in the NHC tropical weather outlook by my next update.


Update…as of 8 PM EDT the NHC has removed this system from their tropical weather outlook.

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

IOH 24 Hr Outlook (1800Z Aug 5)...0% chance of tropical cyclone formation (west of the Republic of Cabo Verde Islands near 15N-27W)


AREA OF INTEREST #2...The frontal surface low pressure along the coastal southeastern United States as of 1800Z was centered between Cape Fear and Cape Lookout on the North Carolina coast based on true-color satellite animation. The circulation is also elongated north-south with low amounts of thunderstorm activity which indicates the non-tropical nature of this system as it’s supported by the elongated eastern divergence zone of the upper trough over eastern North America. This system is essentially out of time to develop a tropical core of thunderstorms as it will arrive to cooler waters in 24 hours while continuing north in the deep-layer southerly flow between the upper trough and west Atlantic upper ridge and west side of the Atlantic surface ridge. Even though tropical development is not anticipated…heavy rainfall with flash flooding potential will spread across the coastal northeastern United States over the next day or so. I plan this to be my final statement on this system on this blog.

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

IOH 24 Hr Outlook (1800Z Aug 5)...0% chance of tropical cyclone formation (offshore of New Jersey near 39.5N-72.5W)


AREA OF INTEREST #3...More recent satellite image of the current western Africa tropical wave of low pressure...taken at 0000Z...with an estimated center of lowest pressure at the red plus (near 12N-12.5W):

The vigorous tropical wave of low pressure that was over central Africa has moved into Western Africa…and continues to produce strong thunderstorms on its west side and has also become better organized. Despite this…a comparison of the 12Z cycles of the GFS and ECMWF between yesterday and today reveals a downward trend in the forecast intensity of this system once it moves into the Atlantic…with the 12Z ECMWF now showing a broad low pressure instead of a tropical depression…and the 12Z GFS showing a tropical depression instead of a bonafide tropical cyclone. An examination of those solutions shows a more north position near 15N latitude and also a large circulation…which could cause this wave to ingest dry Saharan air located to the north. These solutions seem plausible given the latest center fix in the above satellite picture being already at 12N latitude….further north than yesterday. Therefore my updated outlook below has slightly lower odds than the NHC as of this writing…with my outlook having 35% odds of tropical cyclone formation by day 5 while the NHC is at 40%.


It should be noted that other than dry Saharan air and cooler waters north of 15N latitude in the eastern tropical Atlantic…conditions are otherwise favorable for development with low shear and upper outflow supplied by an expansive upper ridge in the region. Therefore if this system manages to stay south of the dry air and cooler water…we could have a bonafide tropical cyclone out of this system in the coming days. Regardless of tropical cyclone formation or not…this wave could bring heavy rains to the Republic of Cabo Verde Islands by Friday.

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

IOH 24 Hr Outlook (1800Z Aug 5)…0% chance of tropical cyclone formation (west coast of Africa near 12N-17.5W)

IOH 48 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 72 Hr Outlook (1800Z Aug 7)…20% chance of tropical cyclone formation (southwest of the Republic of Cabo Verde Islands near 13N-27.5W)

IOH 96 Hr Outlook (1800Z Aug 8)…25% chance of tropical cyclone formation (eastern tropical Atlantic near 13.5N-32.5W)

IOH 120 Hr Outlook (1800Z Aug 9)…35% chance of tropical cyclone formation (eastern tropical Atlantic near 14N-37.5W)


AREA OF INTEREST #4…A rather large tropical wave of low pressure that has been moving through the eastern and central tropical Atlantic is currently passing 44W longitude. The tropical wave was large enough that it left behind a surface trough of low pressure to the east…the feature that is area of interest #1 in this update. The NHC has introduced this wave into their tropical weather outlook even though the usually more reliable GFS and ECMWF do not develop this wave (only the CMC and NAVGEM suggest development of this wave during the past 12Z cycle of model runs). Negatives that go against this wave is a dry Saharan air surge that it helped waft into the Atlantic…which has inhibited thunderstorms in the north half of the wave…and the large broad circulation which makes it challenging for the consolidation needed for tropical development. These negative reasons could be why the GFS and ECMWF do not develop the wave. However given the recent increase in a focused area of thunderstorms and spin near 10N-44W in satellite animation…and the expansive tropical upper ridging forecast in the coming days which will keep shear low and upper outflow high…I now agree with the NHC low development odds of 20% despite the absence of support from the GFS and ECMWF


At this time…I disagree with how far north the NHC forecast track takes this wave in their tropical weather outlook….(1) the Atlantic surface ridge is forecast to be expansive….(2) the west Atlantic upper vortex is forecast to weaken while cut-off from high-latitude cold air…(3) as the central Atlantic upper vortex retrogrades west and a portion of the current eastern North America upper trough slides into the northwest Atlantic…the surface ridge weaknesses associated with these features are forecast to remain well to the north. That means this tropical wave could cross the Lesser Antilles by days 4 and 5…but there is no guarantee of significant impacts at this time as the wave does not currently have a high chance of development.

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

IOH 24 Hr Outlook (1800Z Aug 5)…5% chance of tropical cyclone formation (central tropical Atlantic near 10.5N-48W)

IOH 48 Hr Outlook (1800Z Aug 6)…10% chance of tropical cyclone formation (central tropical Atlantic near 11N-52W)

IOH 72 Hr Outlook (1800Z Aug 7)…20% chance of tropical cyclone formation (east of the Lesser Antilles near 11.5N-56W)

IOH 96 Hr Outlook (1800Z Aug 8)…20% chance of tropical cyclone formation (just east of the southern Lesser Antilles near 12N-60W)

IOH 120 Hr Outlook (1800Z Aug 9)…20% chance of tropical cyclone formation (eastern Caribbean Sea near 12.5N-64W)


...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...no tropical cyclone formation shown

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

**For area of interest #3...tropical wave of interest emerges from Africa and into the eastern tropical Atlantic at 42 hours...develops a low pressure spin near 14.5N-20W at 60 hours...low pressure loses a defined center and becomes broad while passing south of the Republic of Cabo Verde Islands by 66 hours...tropical wave loses broad spin while passing 35W longitude at 138 hours.

**For area of interest #4...tropical wave develops a low pressure spin near 17.5N-55.5W at 126 hours.


1200Z ECMWF Model Run...

**For area of interest #1...no tropical cyclone formation shown

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

**For area of interest #3...tropical wave of interest emerges from Africa and into the eastern tropical Atlantic by 48 hours...develops a broad low pressure spin near 12.5N-26W at 72 hours...broad low pressure reaches 12.5N-37.5W at 120 hours.

**For area of interest #4...no tropical cyclone formation shown


1200Z GFS Model Run...

**For area of interest #1...no tropical cyclone formation shown

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

**For area of interest #3...tropical wave of interest emerges from Africa and into the eastern tropical Atlantic by 39 hours...low pressure spin associated with the wave becomes better defined near 13N-22W at 66 hours...low pressure moves west-northwest across the southern Republic of Cabo Verde Islands at 78 hours...turns more west in track and reaches 15.5N-34W by 120 hours as a possible tropical depression.

**For area of interest #4...no tropical cyclone formation shown


1200Z NAVGEM Model Run...

**For area of interest #1...Surface trough develops a better-defined spin just southwest of the Republic of Cabo Verde Islands over the next 6 hours...while turning west its track slows while tugged by the tropical wave associated with area of interest #3 approaching from the east...the tropical wave associated with area of interest #3 absorbs this area of interest at 102 hours while this area of interest reaches 32.5W longitude.

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

**For area of interest #3...tropical wave develops a low pressure spin centered over the southwestern Republic of Cabo Verde Islands at 102 hours...while in a fujiwhara interaction with area of interest #4 located to the west the low pressure spin moves west-northwest and develops into a tropical cyclone near 18N-34W by 162 hours.

**For area of interest #4...remains genrally stationary with a slow eastward drift through 72 hours due to the tugging effect of areas of interest #1 and #3 off to the east...develops a low pressure spin at 78 hours near 12.5N-43W at 78 hours...remains generally stationary thorugh 150 hours due to fujiwhara interaction with area of interest #3 located to the east while developing into a tropical cyclone.

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