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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 2023 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #70

*******Note that forecast 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 SEPTEMBER 6 2023 1:30 AM EDT...

The Atlantic tropics are expected to remain quiet active over the next several days... see the sections below all current active tropical cyclones and areas of interest. The largest concern in the Atlantic basin is newly-formed Tropical Storm Lee which is expected to be an intense hurricane near the northeastern Caribbean Islands by this weekend.


In addition to the current areas of interest listed below... some model runs insist that an additional strong troipcal wave of low pressure may emerge from western Africa behind Area of Interest #32 in about three to four days. Current METEOSAT satellite imagery (https://www.goes.noaa.gov/f_meteo.html) does not yet show a well-defined robust tropical wave trackable over Africa at this time... however should this change another area of interest may need to be added in future updates.


TROPICAL STORM LEE... The organizing central Atlantic tropical wave of low pressure has progressively strengthened into tropical depression thirteen and then Tropical Storm Lee within the last 24 hours. Lee is expected to continue west-northwest across the Atlantic tropics as the Atlantic surface ridge has begun to recover under the western convergence zone of the current northeast Atlantic upper vortex... with the north angle in the track being a result of the gradual rate of recovery of the ridge followed by the lingering surface ridge weakness of ex-Idalia by the middle of the 5-day forecast period. Lee has continued moving a little faster to the west than the previous forecast and my updated one below is adjusted accordingly... however the models insist on slowing down Lee to the more typical 5W longitude per day clip perhaps due to the ridge weakness of ex-Idalia and so my forecast track eventually shows this pace. By day 5 I remain south of the model consensus for two reasons... (1) ex-Idalia dissipates while completing its post-mature phase as a frontal cyclone decaying below the non-divergent core of its upper trough... (2) the surface and upper level southerly flow associated with the next frontal system and its upper trough in the mid-latitudes will be over the eastern US by day 5 and well off to the west such that I only anticipate the beginning of a northward turn on day 5 once Lee nears the upper southerly flow. However out of respect for the models which have trended northward... and because Lee is also a little north of the previous forecast... my updated forecast track is nudged northward. Regarding intensity... Lee is a little stronger than my previous forecast and so my updated one is increased... especially consideirng Lee will be traversing a large region of warm waters across the Atlantic tropics while remaining parked under vast tropical upper ridging (low shear and outflow) through day 5. My updated forecast intensity is quiet similar to the NHC 11 PM EDT forecast... the only difference is I try to anticipate when an eye wall replacement cycle might occur which albeit is difficult to predict. I speculate that Lee will vault into category 4 status between 48 and 72 hours... with an eye wall replacement cycle keeping the intensity flat from 72 to 96 hours... followed by another burst of intensification to a higher-end category 4 by 120 hours once the eye wall replacement finishes. Interests across the northern Lesser Antilles... Virgin Islands... and Puerto Rico need to monitor this system as it could be very near the islands as a major hurricane this weekend. Given the current forecast track and intenisty... expect coastal surf to also reach the shores of the northern Dominican Republic coast and eastern Bahamas by this weekend.

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

0 Hr Position (0000Z Sep 6)... 50 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 13.5N-43W

IOH 24 Hr Forecast (0000Z Sep 7)... 75 mph maximum sustained wind hurricane centered in the central tropical Atlantic at 14.5N-48.5W

IOH 48 Hr Forecast (0000Z Sep 8)... 105 mph maximum sustained wind hurricane centered in the central tropical Atlantic at 15.5N-53.5W

IOH 72 Hr Forecast (0000Z Sep 9)... 130 mph maximum sustained wind major hurricane centered east of the northern Lesser Antilles at 16.8N-57.5W

IOH 96 Hr Forecast (0000Z Sep 10)... 130 mph maximum sustained wind major hurricane centered just north of the northern Lesser Antilles at 18.8N-62W

IOH 120 Hr Forecast (0000Z Sep 11)... 150 mph maximum sustained wind major hurricane centered north of Puerto Rico at 21N-66W

******National Hurricane Center (hurricanes.gov) official forecast as of 11 PM EDT***************************

5-day Position (0000Z Sep 11)... 150 mph maximum sustained wind major hurricane centered in the western Atlantic at 22.5N-65W


AREA OF INTEREST #32... The tropical wave of low pressure currently offshore of Africa has gradually seen an increase in organization with better defined thunderstorm bands in the western half of its low pressure spin... therefore I have begun a tropical cyclone formation forecast with a specific track and intensity projection as outlined below. Noting this system is currently centered a little south of my previous forecast track and so my updated one is adjsuted accordingly. This system is expected to move slowly over/near the Republic of Cabo Verde Islands thru 48 hours as the east end of the steering Atlantic surface ridge is kept weak by ex-Franklin. Afterwards a westward motion pulling away from the islands is expected as it reaches the same recovering Atlantic surface ridge that Lee will be moving westward under the influence of. By day 5 this system will likely be strong/tall enough to be influenced by upper southerlies on the southeast side of the current central Atlantic upper vortex and so some northward angle is shown in the forecast track during that timeframe. For intensity... I show a more gradual intensification rate than I do with Lee as multiple models insist on keeping this system a broad low pressure area instead of a consolidated tropical cyclone... the broadness is likely a result of this system absorbing the remnants of Katia incoming from the north followed by interaction with the eastern divergence zone of the central Atlantic upper vortex that expands this system's low pressure field. From days 4 to 5 I show no additional intensification due to possible southerly shear when this system reaches the upper southerly flow near the upper vortex. Interests across the Republic of Cabo Verde Islands should monitor the progress of this system... and regardless of tropical cyclone formation or not heavy rainfall and gusty winds are likely for the islands over the next couple of days.

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

0 Hr Position (0000Z Sep 6)... Tropical low centered offshore of Africa at 11N-19W

IOH 24 Hr Forecast (0000Z Sep 7)... Tropical low centered southeast of the Republic of Cabo Verde Islands at 12.5N-22W

IOH 48 Hr Forecast (0000Z Sep 8)... 40 mph maximum sustained wind tropical storm centered southwest of the Republic of Cabo Verde Islands at 13.5N-26W

IOH 72 Hr Forecast (0000Z Sep 9)... 60 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 14N-31W

IOH 96 Hr Forecast (0000Z Sep 10)... 75 mph maximum sustained wind hurricane centered in the eastern tropical Atlantic at 15N-36W

IOH 120 Hr Forecast (0000Z Sep 11)... 75 mph maximum sustained wind hurricane centered in the central tropical Atlantic at 17.5N-40.5W

******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT*****************************

Formation chance through 48 hours...30%

Formation chance through 7 days (168 hours)...60%


AREA OF INTEREST #33 (REMNANTS OF FRANKLIN)... The remnant frontal cyclone of Franklin is now fully entangled with another frontal low and its upper vortex to the east. The frontal low has moved northwest away from Portugal while orbiting around ex-Franklin... and likewise ex-Franklin has pivoted southeastward into the waters northeast of the Azores near 40N-22W as of 0000Z while orbiting around the frontal low. Going forward... ex-Franklin is slated to make multiple cyclonic laps around the edge of the overhead upper vortex while the vortex itself drifts east while kicked by north fractures of the current central North America upper trough and current western Atlantic upper trough. The current position of ex-Franklin places it closer to the periphery of the upper vortex where upper air temps are a little warmer (200 mb heights of 1212 dekameters instead of near 1200 dekameters at the core of the vortex)... which puts it at a disadvantage for thunderstorm re-development and subtropical cyclone formation given that ex-Franklin will be moving over 22 to 23 deg C waters... with water temps as low as 20 deg C by 48 hours when ex-Franklin is at the north apex of its first cyclonic lap. Therefore in this update I have lowered my peak odds of subtropical cyclone formation to 20%. Even though ex-Franklin returns to warmer 22 to 23 deg C waters by 72 and 96 hours... I lower odds of development to 10% as ex-Franklin will be exposed to the potentially suppressing western convergence zone of the overhead upper vortex at 72 hours. Although ex-Franklin lifts northeastward into the more supportive eastern divergence zone of the upper vortex in its second cyclonic lap by 120 hours... it will be back over cooler 20 deg C waters and so I keep development odds capped at 10% for that timeframe. Regardless of subtropical cyclone formation or not... expect coastal surf for the Azores... Portugal... northwest Spain... and the Canary Islands over the next few days until ex-Franklin weakens.

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

IOH 24 Hr Outlook (0000Z Sep 7)... 20% chance of subtropical cyclone formation (northeast Atlantic near 42.5N-15W)

IOH 48 Hr Outlook (0000Z Sep 8)... 20% chance of subtropical cyclone formation (northeast Atlantic near 46N-16W)

IOH 72 Hr Outlook (0000Z Sep 9)... 10% chance of subtropical cyclone formation (east-northeast of the Azores near 42.5N-19W)

IOH 96 Hr Outlook (0000Z Sep 10)... 10% chance of subtropical cyclone formation (northeast Atlantic near 40N-15W)

IOH 120 Hr Outlook (0000Z Sep 11)... 10% chance of subtropical cyclone formation (northwest of northwestern Spain near 45N-14W)

******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT*************************

Formation chance through 48 hours...10%

Formation chance through 7 days (168 hours)...10%


...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/).


1200Z (Sep 5) CMC Model Run...

**For Tropical Storm Lee... reaches 22N-60W at 120 hours as an intense hurricane.

**For Area of Interest #32... passes over the southern Republic of Cabo Verde Islands thru 48 hours as a tropical low with tropical cyclone formation suggested just west of the islands at 54 hours... tropical cyclone reaches 21N-40.5W at 120 hours

**For Area of Interest #33... ex-Franklin circles around periphery of overhead upper vortex and begins to weaken near 49N-17.5W at 66 hours while reaching the northwestern convergence zone of the vortex... dissipates near 47.5N-19W at 78 hours.

**Additional tropical wave emerges from west coast of Africa at 78 hours... tropical cyclone formation suggested near 10.5N-35W at 168 hours

**Additional strong tropical wave emerges from western Africa at 150 hours... located southeast of the Republic of Cabo Verde Islands at 168 hours.


1200Z (Sep 5) ECMWF Model Run...

**For Tropical Storm Lee... reaches 22N-60W at 120 hours as an intense hurricane.

**For Area of Interest #32... passes over the southern Republic of Cabo Verde Islands thru 42 hours as a broad tropical low... north side of the tropical low consolidates near 20.5N-41W by 120 hours.

**For Area of Interest #33... ex-Franklin circles around periphery of overhead upper vortex and begins to weaken near 44N-20W at 84 hours while reaching the western convergence zone of the vortex... the weakening surface low reaches the waters east of the Azores and near 38.5N-19W by 120 hours.

**Additional tropical wave emerges from west coast of Africa at 114 hours... passes just south of the Republic of Cabo Verde Islands as a broad tropical low through 144 hours.


1800Z (Sep 5) GFS Model Run...

**For Tropical Storm Lee... reaches 22N-64W at 120 hours as an intense hurricane.

**For Area of Interest #32...passes over the southern Republic of Cabo Verde Islands thru 42 hours as a tropical low... tropical low reaches 19N-41.5W through 120 hours.

**For Area of Interest #33... ex-Franklin circles around periphery of overhead upper vortex and begins to weaken near 46N-20W at 66 hours while reaching western convergence zone of the vortex... the weakening surface low reaches 40.5N-16W through 120 hours.


1800Z (Sep 5) NAVGEM Model Run...

**For Tropical Storm Lee... reaches 20.5N-64W at 120 hours as an intense hurricane.

**For Area of Interest #32... passes over the southern Republic of Cabo Verde Islands thru 42 hours as a tropical low... tropical low reaches 19N-39W through 120 hours.

**For Area of Interest #33... ex-Franklin circles around periphery of overhead upper vortex and begins to weaken near 47.5N-17W at 66 hours while reaching the northwestern convergence zone of the vortex... the weakening surface low reaches 40N-16W through 120 hours.

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