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 #90

*******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 AUGUST 24 2021 11:55 PM EDT...


See area of interest #1 through #3 sections below for the latest on tropical wave activity across the Atlantic basin... area of interest #3 poses concern for affecting land areas while forecast to be near Nicaragua... Honduras... Belize... and the Mexican provinces of Quintana Roo… Campeche… and Yucatan in the 2 to 4 day window.


Elsewhere… an area of disturbed weather has formed just northeast of the Bahamas with the support of upper vorticity in the region. While moving westward… this disturbance may produce heavy rainfall for the Bahamas and south Florida in the coming days… see area of interest #4 section below for details.


In addition... Eastern Pacific tropical storm Marty… which formed from the remnants of Atlantic tropical cyclone Grace… has weakened to a cloud swirl remnant low pressure while reaching cooler water well west-southwest of the Baja California peninsula.


AREA OF INTEREST #1... The large tropical wave of low pressure now located in the central tropical Atlantic is currently passing 50W longitude. The broad north circulation of the wave and what was the more defined rotation on the east side of the wave have fused into one north-south elongated circulation. The north part of the elongated circulation is in the process of separating from the rest of the wave as a low pressure spin (located near 23N-50W) while bending more north in track while gravitated toward the surface ridge weakness induced by area of interest #4 to the west and northeast Atlantic frontal low. After 48 hours… the current shortwave upper trough over eastern Canada and also the upper vorticity currently near the remnants of Henri will be in the North Atlantic... driving a cold front that creates a surface ridge weakness that traps this system into an east to northeast track.


On the east side of the wave and northern surface low pressure being monitored for development… thunderstorm activity has increased due to divergence on the east side of a nearby upper vortex. However this activity is not well-organized… and so I have lowered development odds in the short-term. By 48 hours the upper vortex will have retrograded westward out of the way due to the expansion of the west Atlantic upper ridge across the mid-latitudes… with this upper ridging supplying low shear and upper outflow for the surface low pressure to potentially develop. However this window of favorable upper winds could quickly end at 72 hours as some of the upper vorticity that is near ex-Henri will be near this system and potentially shear it. By 96+ hours… the upper vorticity and also the upper trough that is currently over western Canada is expected amplify to the northwest of this disturbance… reducing the shear and increasing the upper divergence… and this is when models strongly agree on tropical developing occurring… with some suggestions of rapid intensification into a hurricane by day 5. Thus I agree with the NHC raising development odds to 70% by day 5.

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

IOH 24 Hr Outlook (1800Z Aug 25)… 10% chance of tropical cyclone formation (central Atlantic near 26N-56W)

IOH 48 Hr Outlook (1800Z Aug 26)… 30% chance of tropical cyclone formation (southeast of Bermuda near 30N-60W)

IOH 72 Hr Outlook (1800Z Aug 27)… 40% chance of tropical cyclone formation (central

Atlantic near 32N-56W)

IOH 96 Hr Outlook (1800Z Aug 28)… 60% chance of tropical cyclone formation (central Atlantic near 32N-50W)

IOH 120 Hr Outlook (1800Z Aug 29)… 70% chance of tropical cyclone formation (central Atlantic near 35N-45W)


AREA OF INTEREST #2... The tropical wave of low pressure in the eastern Atlantic has remained organized while retaining thunderstorm banding features on the west side of its low pressure spin located near 10N-29W. Due to lack of computer model support… the NHC has lowered development odds. However I retain 50% odds of development which I think is a good compromise between the wave’s healthy structure and lack of model support. The south position away from dry Saharan air and favorable widespread tropical upper ridging with low shear and upper outflow are other favorable factors. By days 3 to 5… an upper vortex is forecast to become cut-off from the current North Atlantic upper trough as the current west Atlantic upper ridge expands across the mid-latitudes... placing the vortex just northwest of this wave. I have increased the north angle in track as this system could develop a stronger/taller structure more steered by the upper vortex. Even a shallower/weaker system would also be coaxed more north in track due to the forecast surface ridge weakness to be induced by area of interest #1. Another note in regards to the forecast track… I have shifted the points west due to the current position of the low pressure spin relative to the previous forecast. I taper the odds down from the 50% peak by days 4 and 5 as this system crosses the as the southwest side of the upper vortex where upper northwesterly flow would negatively shear this system.

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

IOH 24 Hr Outlook (1800Z Aug 25)… 50% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-34W)

IOH 48 Hr Outlook (1800Z Aug 26)… 50% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-39W)

IOH 72 Hr Outlook (1800Z Aug 27)… 50% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-43W)

IOH 96 Hr Outlook (1800Z Aug 28)… 30% chance of tropical cyclone formation (central tropical Atlantic near 15N-47W)

IOH 120 Hr Outlook (1800Z Aug 29)… 10% chance of tropical cyclone formation (central tropical Atlantic near 18N-50.5W)


AREA OF INTEREST #3... A tropical wave of low pressure is currently crossing the southeastern Caribbean Sea with thunderstorm squalls enhanced by poleward outflow streaming into the current west Atlantic upper vorticity near the Bahamas. The thunderstorm squalls became better organized this past afternoon before becoming a bit less organized tonight. Models remain in agreement on developing this wave as it moves across the southern Caribbean and encounters an expanding upper ridge with low shear and upper outflow to develop in the wake of the upper vorticity as the vorticity weakens while remaining cut-off from high-latitude cold air. I have assigned lower odds of development for the short-term as the squalls become a bit less organized tonight as noted above. However for the long term… I am slightly higher than the NHC… at 70%… due to the strong model support that has remained in place. Note the Forecast track angle has a more north component by 2 to 5 days as the tropical wave rounds the southwest side of the Atlantic surface ridge. This forecast track takes the wave across the Yucatan peninsula between the days 4 and day 5 position… therefore I dip odds of development to 50% at the day 5 point due to the land interaction. Note however the upper air environment across the Gulf of Mexico will remain favorable for development with widespread upper ridging featuring low shear and upper outflow… so development odds once this wave moves away from the Yucatan and across the western Gulf of Mexico are expected to be high if this wave has not developed into a tropical cyclone before that point.


Interests in Nicaragua... Honduras... Belize... and the Mexican provinces of Quintana Roo… Campeche… and Yucatan should be closely monitoring this wave as it will be in the region by days 2 to 4 as a possible tropical cyclone.

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

IOH 24 Hr Outlook (1800Z Aug 25)… 0% chance of tropical cyclone formation (South-Central Caribbean Sea near 13N-75W)

IOH 48 Hr Outlook (1800Z Aug 26)… 30% chance of tropical cyclone formation (east of northern Nicaragua near 14N-80W)

IOH 72 Hr Outlook (1800Z Aug 27)… 50% chance of tropical cyclone formation (just offshore of northeast Honduras near 15.5N-84W)

IOH 96 Hr Outlook (1800Z Aug 28)… 70% chance of tropical cyclone formation (just offshore of northern Belize near 17.5N-87.5W)

IOH 120 Hr Outlook (1800Z Aug 29)… 50% chance of tropical cyclone formation (just offshore of the northwest Yucatan peninsula near 20.5N-91W)


AREA OF INTEREST #4…Upper vorticity that has been lingering near the Bahamas through its eastern divergence zone has produced increased showers and thunderstorms on its northeast side and northeast of the islands… a surface trough of low pressure near 22.5N-70W just east of the islands defined in ASCAT passes… and a mid-level spin over the southeast Bahamas defined in the CIMSS 850 mb vorticity product (http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=atlantic&sat=wg8&prod=vor&zoom=&time=). With the cool core upper vorticity forecast to dissipate after 48 hours while cut-off from high-latitude cold air… upper winds will become increasingly conducive for tropical development of the mid-level and surface features while left in widespread upper ridging with low shear and upper outflow across the west Atlantic… Gulf of Mexico… and southern US. Therefore I have added this disturbance as an area of interest even though it currently has no model support.


Forecast track for the first 48 hours is to follow the supportive eastern divergence zone of the upper vorticity which will be retrograding west around the aforementioned upper ridging. After that time I forecast a west-northwest track around the southwest side of the Atlantic surface ridge and northeast side of area of interest #3. On this forecast track… this disturbance could bring heavy rains to the Bahamas and south Florida in the coming days before entering the northeast Gulf of Mexico by day 5. Despite the above-mentioned forecast improvement in the upper winds… I only assign low 10% odds of development as this system will likely be competing for surface inflow with area of interest #3. It is conceivable this disturbance simply merges with the north side of area of interest #3 instead of developing on its own… which could make area of interest #3 grow into a large broad disturbance and potentially cause it to have a more north position and track than currently forecast.

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

IOH 24 Hr Outlook (1800Z Aug 25)… 5% chance of tropical cyclone formation (southeastern Bahamas near 22.5N-72.5W)

IOH 48 Hr Outlook (1800Z Aug 26)… 10% chance of tropical cyclone formation (central Bahamas near 22.5N-75.5W)

IOH 72 Hr Outlook (1800Z Aug 27)… 10% chance of tropical cyclone formation (southwest of Andros Island of the western Bahamas near 24N-79W)

IOH 96 Hr Outlook (1800Z Aug 28)… 10% chance of tropical cyclone formation (just west of the Florida Keys near 24.8N-82.5W)

IOH 120 Hr Outlook (1800Z Aug 29)… 10% chance of tropical cyclone formation (northeast Gulf of Mexico near 27.5N-86W)


...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 cyclone formation suggested near 30N-56W at 42 hours... hurricane strength suggested while system turns east in track and reaches 31.5N-56W at 60 hours...intense hurricane strength suggested near 32.2N-51.5W at 120 hours.

**For area of interest #2... no development shown

**For area of interest #3... tropical cyclone formation suggested just south of western Cuba near 20.5N-85W at 78 hours... passes just offshore of the north Yucatan coast through 102 hours... strengthens in the western Gulf of Mexico into a large hurricane near 25N-94W by 120 hours.

**For area of interest #4... no development shown

**Strong tropical wave forecast to emerge from Africa at 150 hours... tropical cyclone formation suggested in long range due south of the Republic of Cabo Verde Islands.


1200Z ECMWF Model Run...

**For area of interest #1...Tropical cyclone formation suggested near 32N-53W at 72 hours... hurricane strength suggested near 33.8N-47.5W at 120 hours as system turns northeast in track.

**For area of interest #2... no development shown

**For area of interest #3... develops into a broad low pressure spin that crosses Central America and southeastern Mexico at 72 to 96 hours... north end of broad low pressure forecast to develop into a tropical cyclone just offshore of the Louisiana coast near 28N-92.5W at 144 hours.

**For area of interest #4... no development shown

**Strong tropical wave forecast to emerge from Africa between 120 and 144 hours... tropical cyclone formation suggested in long range due south of the Republic of Cabo Verde Islands.

1200Z GFS Model Run...

**For area of interest #1... tropical cyclone formation suggested near 32N-52.5W at 96 hours... strengthens into a high-end tropical storm located near 33N-48W at 120 hours.

**For area of interest #2... no development shown

**For area of interest #3... tropical cyclone formation suggested as system makes landfall near the Belize/Mexico border on the east Yucatan coast near 17.8N-88W at 99 hours... by 120 hours the weakened and broad tropical cyclone located in the eastern Bay of Campeche near 21N-93W at 120 hours.

**For area of interest #4... no development shown


1200Z NAVGEM Model Run...

**For area of interest #1... tropical cyclone formation suggested near 31.5N-53W at 66 hours... by 120 hours becomes a strong hurricane near 32.2N-48W.

**For area of interest #2... no development shown

**For area of interest #3... tropical cyclone formation shown in the southwest Gulf of Mexico near 22N-96W at 150 hours

**For area of interest #4... no development shown

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