MY 2021 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #118
*******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 SEPTEMBER 22 2021 5:15 AM EDT...
The Atlantic tropics remain active with multiple
systems to watch:
**See Tropical Depression Peter and Rose sections below for an update on the two currently active storms in the Atlantic basin. Note that although Peter may weaken to a remnant trough soon… interests in Bermuda should be aware that Peter could re-organize and relocate closer to the island by Thursday… or alternatively could be affected by a new subtropical or tropical low that takes Peter’s place. See Peter section below for more details.
**See Odette (area of interest #1) section below for an update on the remnant cyclone in the open north Atlantic which may re-acquire tropical character
**See area of interest #2 section below for an update on the latest tropical wave of low pressure in the eastern tropical Atlantic… it’s potential to develop into a strong tropical cyclone is high.
Elsewhere… some long range model runs indicate that another tropical wave of low pressure could emerge from Africa and attempt to develop east of area of interest #2 in the coming days… due to the forecast stout presence of the eastern tropical Atlantic upper ridge with low shear and upper outflow.
TROPICAL DEPRESSION PETER… While passing just north of Puerto Rico… Peter has begun to succumb to ongoing southwesterly shear while weakening to a tropical depression. Also the size of the sheared off thunderstorm bursts has been shrinking in size with time. The shear is expected to worsen in the next 24 hours as the current North Atlantic upper trough deposits upper vorticity just to the northwest. Therefore my updated forecast below assumes Peter will not survive the next 24 hours if it has not done well with the currently lower shear levels. The updated forecast track is nudged south and east due to Peter’s current position.
The future of Peter after 24 hours may be interesting to watch… even if it loses its status as a tropical cyclone in the short-term. One possibility is that Peter reforms to the northeast close to Bermuda as a subtropical or tropical low in an upper divergence maximum and lower shear region to develop once the upper vorticity weakens to an upper vortex. The other possibility… championed by the GFS…is that Peter stays southwest of the upper vortex while a new subtropical or tropical surface low develops closer to Bermuda. The GFS scenario could get more complicated if Peter makes a comeback in upper anticyclonic flow with lower shear/upper outflow which may develop in the environment southwest of the upper vortex… which may result in Peter and the separate subtropical or tropical low orbiting each other in a fujiwhara type of interaction.
With these forecast updates:
**Interests in the northern Lesser Antilles… Virgin Islands… Puerto Rico… the Dominican Republic… and the Bahamas are less likely to see coastal sea swells as Peter has weakened to a tropical depression
**Interests in Bermuda should be aware of developments that could occur even if Peter loses tropical cyclone status in the short term.
Heavy rains and gusty winds are possible Thursday or Friday from a Peter that re-generates and re-organizes close to the island… or from a separate subtropical or tropical low that could form even if what is left of Peter stays to the southwest this week.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Sep 22)… 35 mph maximum sustained wind tropical depression centered northwest of Puerto Rico at 20.8N-65.3W
IOH 24 Hr Forecast (0000Z Sep 23)… remnant trough located east-northeast of the eastern Bahamas at 22.5N-69.5W
TROPICAL STORM ROSE (RECENTLY DOWNGRADED TO TROPICAL DEPRESSION ROSE)… Rose continues its northwest track into the open eastern Atlantic due to the drag of upper southwesterly flow out ahead of upper vorticity in the northeast Atlantic. This track will also continue as Rose tracks toward Odette’s surface ridge weakness. The track by 72 hours turns northeast east as the latest model guidance shows Odette accelerating southeast by that time.
Regarding intensity… as forecast yesterday the tropical storm has weakened to a depression in the southwesterly shearing upper winds out ahead of the northeast Atlantic upper vorticity. Once Rose moves past the axis of the shearing upper vorticity and move into a haven of lower shear at 24 to 48 hours… I project Rose to regain storm strength. By 72 hours Rose will near an upper westerly jet on the south side of the upper vortex tied to Odette… thus I project that Rose will weaken to a remnant low by that time as the shear from the jet will likely be too much for Rose to handle. Some models indicate Rose’s remnants making a comeback in the eastern divergence zone of the upper vortex while turning north in a fujiwhara interaction with Odette. However Rose would be positioned east of Odette in such an interaction… where waters are cooler and thus Rose would likely not be tropical in nature in this comeback scenario.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official
0 Hr Position (0000Z Sep 22)… 35 mph maximum sustained wind tropical depression centered at 22.9N-37.9W
IOH 24 Hr Forecast (0000Z Sep 23)… 40 mph maximum sustained wind tropical storm centered at 25N-40W
IOH 48 Hr Forecast (0000Z Sep 24)… 40 mph maximum sustained wind tropical storm centered at 28N-43W
IOH 72 Hr Forecast (0000Z Sep 25)… Remnant low centered at 31N-41W
AREA OF INTEREST #1 (REMNANTS OF ODETTE)… As of 0000Z… the remnant frontal cyclone of Odette was centered in the open North Atlantic at 40N-40W. Odette’s strength as a remnant frontal cyclone is facilitated by the upper divergence zone of the amplifying upper trough in the north Atlantic. The amplification of the upper trough is being caused by adjacent amplification of warm eastern North America upper ridging to the west in the warm sector of the frontal system now over eastern North America. The upper trough is expected to soon amplify further into an upper vortex to the northwest of Odette… which will cause Odette to whirl northwest into the upper vortex thru 48 hours. By 72+ hours… a portion of the upper trough associated with the eastern North America frontal system is then expected to kick the upper vortex and Odette southeastward into the open eastern Atlantic. The models are split into two camps tonight… one where the cold front of the North American upper trough fragment simply absorbs Odette… the other which has shifted south and brings Odette to warmer 26+ deg C by 96+ hours as Odette undergoes a fujiwhara interaction with what is to be left of Tropical Storm Rose expected to approach from the southeast. Because the GFS no longer projects the upper vortex to cool down to de-stablizing temps when Odette is over cooler waters… the only potential for Odette to re-acquire tropical character is if it indeed gets flung south to warmer water in the above-mentioned fujiwhara interaction scenario… and all the models are not onboard with that scenario at present. As a result… I have stopped doing subtropical cyclone formation forecasts on Odette’s remnants… and have switched to doing probability outlooks for subtropical cyclone formation.
In addition to not all models not being onboard with Odette making it far south… I have low 30% peak odds of subtropical development by day 5 as any fujiwhara interaction with Rose would push Odette toward the west side of the overhead upper vortex where northerly shear or upper convergence could be factors in limiting subtropical development. On a final note… coastal sea swells may return to the shores of Newfoundland in the next 48 hours as Odette whirls back to the northwest.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Sep 23)… 0% chance of subtropical cyclone formation (north Atlantic near 43N-41W)
IOH 48 Hr Outlook (0000Z Sep 24)…0% chance of subtropical cyclone formation (north Atlantic near 43N-44W)
IOH 72 Hr Outlook (0000Z Sep 25)… 0% chance of subtropical cyclone formation (northeast Atlantic near 40N-39W)
IOH 96 Hr Outlook (0000Z Sep 26)… 20% chance of subtropical cyclone formation (eastern Atlantic near 35N-39.5W)
IOH 120 Hr Outlook (0000Z Sep 27)… 30% chance of subtropical cyclone formation (eastern Atlantic near 31N-39.5W)
AREA OF INTEREST #2…The tropical wave of low pressure in the eastern tropical Atlantic lost thunderstorm activity for much of Tuesday morning and afternoon… perhaps from the dry Saharan air mass lurking to the northeast. It appears tonight the tropical wave has made a comeback with increased and organized thunderstorms tied to its low pressure spin as the wave advances away from the dry air. Over the next five days the forecast track keeps this system under low shear and upper outflow beneath the tropical upper ridge axis… and all models still forecast tropical cyclone formation. Therefore I am continuing tropical cyclone formation forecast as outlined below… with specific track and intensify forecast points.
The prior forecast track has done well… so my updated one remains the same. A slow down the west speed and increase the north angle in the track is anticipated going forward as the Atlantic surface ridge will have a weakness caused by Rose and Odette. However this weakness is not expected to be strong enough to recurve this system north thru 3 days… as both Rose and Odette are expected to weaken in the longer range (see above Rose and Odette sections for the factors expected to weaken each system). The additional slow down and increase in north angle at days 4 and 5 is a reflection of what is forecast to be Peter’s remnants contributing to the weakness. Regarding intensity… unlike the last three storms (Odette… Rose… Peter) this system will be staying away from upper-level shearing winds thru day 5. And with the healthy initial structure of the wave… I forecast a strong hurricane by day 5. With that said… the updated intensity forecast below is nudged down from the previous due to the hiccup this system had with dry air in the last 24 hours.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Sep 22)… Tropical low centered at 10.5N-31W
IOH 24 Hr Forecast (0000Z Sep 23)…40 mph maximum sustained wind tropical storm centered at 11N-36W
IOH 48 Hr Forecast (0000Z Sep 24)… 60 mph maximum sustained wind tropical storm centered at 11.5N-41W
IOH 72 Hr Forecast (0000Z Sep 25)… 80 mph maximum sustained wind hurricane centered at 12N-46W
IOH 96 Hr Forecast (0000Z Sep 26)… 95 mph maximum sustained wind hurricane centered at 14N-49W
IOH 120 Hr Forecast (0000Z Sep 27)… 110 mph maximum sustained wind hurricane centered at 16N-52W
...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 Tropical Depression Peter… weakens to a remnant trough northeast of the eastern Bahamas by 60 hours
**For Tropical Storm Rose… weakens to a remnant low that loses its closed circulation near 27.5N-41.5W at 84 hours
**For Area of Interest #1 (Ex-Odette)…cyclonically loops northwest to 46N-44W thru 48 hours…north part of cold front ejecting from eastern North America absorbs ex-Odette at 41N-40W by 84 hours
**For Area of Interest #2…tropical cyclone formation shown at 11.5N-45W at 84 hours… compact and strong tropical storm at 14N-51W at 120 hours
1200Z ECMWF Model Run...
**For Tropical Depression Peter… weakens to a large broad remnant low south of Bermuda at 72 hours… passes over Bermuda at 96 hours… begins to re-strengthen as a non-tropical frontal cyclone on approach to Nova Scotia at 120 hours
**For Tropical Storm Rose… turns in a large anticyclonic (clockwise) loop and reaches 26N-32.5W at 120 hours while weakening to a remnant low
**For Area of Interest #1 (Ex-Odette)…cyclonically loops northwest to 46N-44W thru 48 hours… north part of cold front ejecting from eastern North America absorbs ex-Odette at a location northwest of the Azores by 96 hours
**For Area of Interest #2…tropical cyclone formation shown at 13N-47.5W by 96 hours becomes a compact hurricane near 14N-49W by 120 hours
1800Z GFS Model Run...
** For Tropical Depression Peter… weakens to remnant trough east of the eastern Bahamas by 27 hours
** For Tropical Storm Rose… weakens to a remnant trough at 84 hours while located near 30N-37W… swings northeast while re-gaining a closed circulation in a fujiwhara interaction with ex-Odette and reaches 33.5N-30W by 120 hours
**For Area of Interest #1 (Ex-Odette)…cyclonically loops northwest to 44N-44W thru 42 hours…accelerates south to 32.5N-41.5W by 120 hours
**For Area of Interest #2…tropical cyclone formation shown at 10N-44W at 69 hours… becomes a compact tropical storm at 13N-51W by 120 hours
**Possible subtropical or tropical low east of Bermuda at 72 hours that cyclonically whirls west into Bermuda by 105 hours… drifts east away from Bermuda thru 120 hours
1200Z NAVGEM Model Run...
**For Tropical Depression Peter… weakens to remnant trough in next 6 hours
**For Tropical Storm Rose… weakens to a remnant low that becomes the dominant in a fujiwhara interaction with ex-Odette… reaches 30N-31W at 120 hours
**For Area of Interest #1 (Ex-Odette)…cyclonically loops northwest to 45N-42.5W thru 42 hours…accelerates southeast and loses identity to Rose’s remnant low at 114 hours
**For Area of Interest #2…tropical cyclone formation at 10N-39W at 66 hours… reaches 13.5N-47W at hurricane strength at 120 hours
**Tropical wave emerges from Africa at 120 hours… tropical cyclone formation suggested at 10N-22W at 156 hours