*******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.**********
...TUESDAY OCTOBER 4 2022 12:59 AM EDT...
The Atlantic tropics remain active as we progress through early October... with multiple areas of interest being monitored for signs of future tropical development:
(1) See area of interest #34 section below for an update on the tropical disturbance in the eastern Atlantic.
(2) The current tropical wave of low pressure in the central tropical Atlantic continues to show signs of organization... and will likely overspread the southern Lesser Antilles... Trinidad and Tobago... and northeastern Venezuela with vigorous weather by late Tuesday and into Wednesday... see area of interest #35 section below for more information.
(3) The broad frontal low pressure area currently offshore of the United States mid-Atlantic coast is consolidating into a frontal cyclone... will monitor the cyclone for potential acquistion of tropical characteristics as it meanders just offshore over the next 48 hours... see area of interest #36 section below for more information.
New to this site this year... I will be sequentially numbering up areas of interest for possible Atlantic tropical development. In this scheme... will reset back to #1 at the start of next year (January 2023). The current areas of interest in this blog post are designated #34 to #36 as the other numbers were used in previous birdseye view posts. This scheme is to reduce confusion as Atlantic tropical activity increases during the peak of the hurricane season... when multiple simultaneous areas of interest begin and end which previously required shuffling around the area of interest numbers from update to update.
AREA OF INTEREST #34...In the eastern tropical Atlantic... a tropical wave of low pressure near 30W longitude to the west and additional tropical wave to the east that approached from the west coast of Africa have merged into a southwest-northeast elongated tropical low pressure system located to the southwest of the Republic of Cabo Verde Islands. The NHC TAFB has re-analyzed the merged system as a single tropical wave with low pressure spin. In recent hours the northeast side of the elongated system appears to be consolidating into an organized spin near 11.5N-27.5W... therefore I have begun a tropical cyclone formation forecast with specific track and intensity forecast points as outlined below.
In the upper-layers and to the northwest of this system... a warm core central Atlantic upper ridge is supported by the warm surface southerly flow ahead of area of interest (AOI) #36. This upper ridge has recently pushed a north Atlantic upper trough southeastward toward this system as a cut-off upper vortex. As AOI #36 and broad frontal to absorb AOI #36 shift northeastward the central Atlantic upper ridge will take a corresponding eastward shift and drive the nearby cut-off upper vortex southwestward and then westward. The eastern divergence zone of the upper vortex is expected to generate an inverted surface trough on the south side of the Atlantic surface ridge that shifts westward with the upper vortex. The forecast track of this system is expected to be northwestward into the open central Atlantic while it chases the inverted surface trough. Intensity wise... the upper vortex will be a double-edged sword for this system. It has potential to enhance its thunderstorm activity through its eastern divergence zone... and also has potential to disrupt this system with southerly wind shear. The intensity forecast below shows gradual strengthening to a category 1 hurricane over the next 72 hours as this system will have some distance from the upper vortex such that the shear is not excessive. A lower steady-state intensity of moderate/high tropical storm strength is then shown at 96+ hours as the forecast track brings this system closer to the upper vortex where shear levels are higher.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Oct 3)...Tropical low centered at 11.5N-27.5W
IOH 24 Hr Forecast (1800Z Oct 4)...45 mph maximum sustained wind tropical storm centered at 13.5N-31W
IOH 48 Hr Forecast (1800Z Oct 5)...60 mph maximum sustained wind tropical storm centered at 16.5N-32W
IOH 72 Hr Forecast (1800Z Oct 6)...75 mph maximum sustained wind hurricane centered at 19N-33.2W
IOH 96 Hr Forecast (1800Z Oct 7)...60 mph maximum sustained wind tropical storm centered at 21.5N-36W
IOH 120 Hr Forecast (1800Z Oct 8)...60 mph maximum sustained wind tropical storm centered at 24N-41W
AREA OF INTEREST #35...The previous fanning upper outflow pattern of the westward-moving central Atlantic tropical wave of low pressure has become suppressed over the last 24 hours as the wave has neared the south side of a nearby upper vortex that is suppressing the northern outflow of the wave. In response... the wave has seen a marked decrease in its thunderstorm squalls. However the wave features a small area of weak rotation and associated skeletal squalls that passed 10N-52.5W as of 1800Z earlier this evening. The position of this rotation is slightly south of my previous forecast track... and my updated one is nudged accordingly. In the short-term this system is still expected to bend slightly north in track toward the surface ridge weakness associated with area of interest (AOI) #36. However later in the forecast period... the ridge weakness closes as the low pressure area associated with AOI #36 lifts out to the northeast... and the forecast track of this system is therefore bent more westward by days 4 and 5. In 5+ days... the current northwest United States upper vortex and an additional southward-digging upper trough from western Canada are expected to merge into an amplified upper trough that settles into eastern North America... with the western convergence zone of the trough expected to build a strong surface ridge over the United States. The long-range result suggests the ridge will likely deflect this system on a west-southwest track toward Nicaragua.
Regarding odds of tropical cyclone formation... I have slightly lowered short-term odds of tropical cyclone formation due to the reduction in this system's organized thunderstorm squalls. The odds are steadily increased through the 5-day forecast period as this system by 48 hours reaches enhancing split flow upper divergence between the southwest side of the nearby upper vortex and southeast side of the current northern Caribbean upper ridge axis. By 72+ hours this system has potential to exhibit healthy southern outflow supported by the upper ridge axis... however the northern outflow could be suppressed as the southern-adjusted track keeps this system south of the upper ridge axis instead of directly below it. The less than ideal long-range upper outflow pattern and reduction in some of the computer model support cause me to keep long-range odds peaked at 50% instead of raising them.
Regardless of tropical cyclone formation or not in the short-term... chances remain high for heavy rainfall and gusty winds for the southern Lesser Antilles... Trinidad and Tobago... and northeastern Venezuela for late Tuesday and into Wednesday. I recommend interests in Nicaragua should monitor the progress of this tropical wave as it has potential to approach the area as a strengthening tropical cyclone this weekend.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Oct 4)...20% chance of tropical cyclone formation (east of the southern Lesser Antilles near 11N-57.5W)
IOH 48 Hr Outlook (1800Z Oct 5)...30% chance of tropical cyclone formation (just west of the southern Lesser Antilles near 12N-62W)
IOH 72 Hr Outlook (1800Z Oct 6)...40% chance of tropical cyclone formation (southeastern Caribbean Sea near 13N-66W)
IOH 96 Hr Outlook (1800Z Oct 7)...50% chance of tropical cyclone formation (central Caribbean Sea near 13.8N-70W)
IOH 120 Hr Outlook (1800Z Oct 8)...50% chance of tropical cyclone formation (central Caribbean Sea near 14N-75W)
AREA OF INTEREST #36...The southern portion of a large-scale cold core eastern North America upper trough has been cut-off into a vortex over the northeastern United States... courtesy of a warm core upper ridge over southeastern Canada that is bolstered by the warm sector of a frontal cyclone currently sliding eastward across northeastern Canada. The broad frontal low pressure that has been offshore of the United States mid-Atlantic coast is in the process of consolidating into a more focused frontal cyclone supported by the more localized upper divergence maximum of the approaching northeastern United States upper vortex. From 24 to 48 hours the frontal cyclone is expected to whirl in a counter-clockwise loop arc and into the center of the upper vortex as a maturing frontal cyclone typically does. Due to the de-stabilizing cold temperatures of the upper vortex (200 mb heights near 1200 dekameters) and close proximity of the warm Gulf stream waters in the vicinity of Cape Hatteras and points south... there is potential for the frontal cyclone to build thunderstorms and acquire tropical characteristics around the 48-hour mark. I set odds of subtropical cyclone formation at a low 20% as the window for subtropical development will be short lived. Specifically soon after 48 hours... the overhead upper vortex begins to race to the northeast which will ultimately leave behind the frontal cyclone and cause it to weaken beneath the western convergent side of the departing upper vortex. Note the forecast track has the frontal cyclone accelerate east-southeast under the west-northwesterly flow of the southwest quadrant of the departing upper vortex...and also the southwest quadrant of a new broad frontal low to be generated by the eastern divergent side of the departing upper vortex. The acceleration of the upper vortex is expected as mid-latitude upper westerly flow in the region markedly increases with the approach of the current northwest US upper vortex and the next southward digging upper trough to approach from western Canada.
Regardless of whether or not the frontal cyclone acquires tropical characteristics the tight pressure gradient between the north side of the frontal cyclone and south side of ongoing surface ridging to the north will prolong coastal surf for the coasts of Delaware... southeastern Maryland... southeastern Virginia... and northeastern North Carolina. If the frontal cyclone becomes a little stronger or tracks a little closer to shore... the current area of breezy winds in the region could increase enough to induce isolated cases of wind damage. The coastal surf and breezy conditions are expected to decline after by late Wednesday.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
ION 24 Hr Outlook (1800Z Oct 4)...0% chance of subtropical cyclone formation (offshore southeastern Maryland and Delaware near 37N-73.8W)
IOH 48 Hr Outlook (1800Z Oct 5)...20% chance of subtropical cyclone formation (offshore of the northeastern North Carolina coast near 35.8N-73.5W)
IOH 72 Hr Outlook (1800Z Oct 6)...0% chance of subtropical cyclone formation (western Atlantic near 35N-69W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Oct 3) CMC Model Run...
**For area of interest #34... over the next 18 hours the broad tropical low pressure system develops two centers (one near 10.5N-32.5W and a second near 14N-29W)... while moving northwestward both centers gradually merge into one near 17.5N-35W by 54 hours... merged circulation gradually evolves into weak tropical cyclone that continues northwest and then west and reaches 26.5N-50W at 120 hours.
**For area of interest #35... tropical cyclone formation suggested in central Caribbean Sea near 14.5N-74W at 108 hours... tropical cyclone gradually strengthens while continuing westward and reaches 15N-77W at 120 hours.
**For area of interest #36... frontal cyclone materializes offshore of southeastern Maryland near 37.5N-74W at 24 hours... while establishing a more circular center becomes a potential subtropical storm near 37N-74W at 48 hours... subsequently circulation turns easward and then east-northeastward while weakening and dissipates near 41N-56W at 102 hours.
1200Z (Oct 3) ECMWF Model Run...
**For area of interest #34... tropical cyclone formation suggested near 16.5N-32.5W at 48 hours... while continuing northwest weakens to a remnant low near 23.8N-39W at 96 hours... remnant low track west-northwest and weakens to a trough near 25.5N-46W at 120 hours.
**For area of interest #35... no development shown
**For area of interest #36... frontal cyclone materializes offshore of southeastern Maryland near 37.5N-74W at 24 hours... drifts southwest to 36.8N-75W through 48 hours... shortly after this time the circulation rapidly weakens and loses definition to new broad frontal low forming to the northeast.
1800Z (Oct 3) GFS Model Run...
**For area of interest #34... tropical cyclone formation suggested near 17.5N-32.5W at 42 hours... weakens to a remnant low near 20.5N-33.5W at 72 hours... remnant low turns west-northwest in track and reaches 25.5N-49W at 120 hours.
**For area of interest #35... tropical wave organizes into broad tropical low to the east of Nicaragua near 12.5N-81W by 168 hours.
**For area of interest #36... frontal cyclone materializes offshore of southeastern Maryland near 37.8N-74W at 21 hours... afterwards the circulation shifts east-southeast while gradually weakening and dissipates near 36N-70W at 66 hours.
1200Z (Oct 3) NAVGEM Model Run...
**For area of interest #34... tropical low becomes well-defined near 13.8N-29W at 24 hours... tropical low moves northwest and then west-northwest into the open central Atlantic and reaches 29N-46W at 120 hours.
**For area of interest #35... gradually organizes into a tropical low which moves west-northwest and reaches the waters southwest of Puerto Rico and southeast of the Dominican Republic by 120 hours
**For area of interest #36... frontal cyclone materializes offshore of southeastern Maryland near 37.5N-74W at 24 hours... circulation subsequently weakens and moves east then east-northeast and dissipates near 40N-63.5W at 84 hours.
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