*******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 OCTOBER 5 2022 4:30 AM EDT...
Tropical Depression Twelve has become the latest tropical cyclone to form in the Atlantic basin... at a location in the eastern tropical Atlantic. See Tropical Depression Twelve section below for more information on the new tropical cyclone. Elsewhere in the Atlantic basin... monitoring multiple areas of interest for signs of future tropical development:
(1) The current tropical wave of low pressure in the central tropical Atlantic continues to show signs of vigor while closing in on northeastern Venezuela and the southern Lesser Antilles... and will likely develop as it moves across the Caribbean Sea for the remainder of the week and the weekend. This system has potential to move toward Nicaragua as a strengthening tropical cyclone in 5+ days... see area of interest #35 section below for more information.
(2) See area of interest #36 section below for an update on the frontal cyclone currently located offshore of the mid-Atlantic United States.
(3) See area of interest #37 section below for information on a persistent surface trough of low pressure in the western Caribbean Sea located between Jamaica and Honduras.
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 #35 to #37 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.
TROPICAL DEPRESSION TWELVE...Although the tropical low pressure area in the eastern tropical Atlantic has become a tropical cyclone as expected... a few changes have occurred that do not favor the health of this system. The circulation has consolidated further to the north and closer to the nearby upper vortex to the northwest... exposing the new tropical depression to stronger shear. The latest model data concerning an eastern North America upper trough to consolidate over the next 72 hours... to materialize from the merger of the current upper trough over the western Dakotas and another diving southeast from western Canada... show the trough being positioned further east... which will position an Atlantic Canada frontal low that it will generate further east and closer to the Atlantic. This will allow the warm sector of the frontal low to keep the central Atlantic warm core upper ridge stronger. Although the upper ridge will still push the upper vortex southwestward and then westward... the stronger upper ridge will keep the vortex further southeast and closer to the depression... thus keeping shear levels higher for the depression. The stronger upper ridge will also stretch out the upper vortex into an elongated vorticity string... resulting in a loss of the vortex's surface-pressure-dropping eastern divergence zone such that the south side of the Atlantic surface ridge is now likely to recover. So although my short-term track forecast is adjusted northward due to the current position of the depression and current weak south side of the Atlantic surface ridge... the longer-term track is adjusted southward while suggesting a turn more to the west as the surface ridge recovers. My updated intensity forecast is also substantially lowered in this update due to the unfavorable shear outlook discussed above... now no longer calling for the depression to become a tropical storm and dissipating it by 72 hours as the updated forecast track and updated upper vortex positioning brings the depression directly into the upper vortex where shear is higher.
Noting that some model runs suggest the depression could re-generate in the long range. These model runs bring the remnants of the depression west-northwest to the other side (north side) of the elongating upper vortex and underneath the southwest side of the central Atlantic upper ridge where shear will be lower and upper outflow will be higher. Since not all models agree on this idea... will need to actually see if in fact this system survives its encounter with the elongating upper vortex in the short-term before making an extended long range forecast that predicts such a re-genesis.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Oct 5)...35 mph maximum sustained wind tropical depression centered at 15.3N-30.4W
IOH 24 Hr Forecast (0000Z Oct 6)...35 mph maximum sustained wind tropical depression centered at
18N-32W
IOH 48 Hr Forecast (0000Z Oct 7)...35 mph maximum sustained wind tropical depression centered at 20.5N-34W
IOH 72 Hr Forecast (0000Z Oct 8)...Remnant trough near 21N-37.5W
AREA OF INTEREST #35...The vigorous central Atlantic tropical wave of low pressure heading toward northeastern Venezuela and the southern Lesser Antilles has made progress despite encountering westerly shear on the south side of the nearby upper vortex... while developing a large area of concentrated thunderstorm activity to the east of its rotation. Although the rotation itself was void of thunderstorm activity due to the shear... on Tuesday morning it was becoming better defined on satellite imagery and aircraft reconnaissance was dispatched to investigate. The resulting recon data did not indicate a well-defined surface center to declare a tropical depression. This system remains on track with the previous forecast track as the area of rotation has gained an increasing north bend in its westward track in response to the surface ridge weakness associated with area of interest (AOI) #36. The forecast track is expected to bend more westward once a major upper trough consolidates over eastern North America... with the trough to kick out the upper vortex supporting AOI #36 northeastward such that the surface ridge weakness closes. The western convergence zone of this upper trough is also expected to build a rather strong surface ridge over the United States... enough to keep the track on a westward or perhaps west-southwest heading toward Nicaragua by 5+ days.
Regarding odds of tropical cyclone formation... this system is expected to move past the the nearby upper vortex and its associated shear and into a lower shear environment on the south side of the northern Caribbean upper ridge axis to persist during the forecast period. In the next 24 hours... this system may also receive a boost while moving into an area of split flow upper divergence between the southwest side of the upper vortex and southeast side of the northern Caribbean upper ridge. Their may already be signs that this system is encountering the more favorable upper winds as thunderstorm activity has increased just south of Barbados where the area of rotation of the tropical wave is currently located. I agree with the NHC raising peak odds of tropical cyclone formation to 80% odds for the next five days... out of respect for this system's tenacity over the last 24 hours... the more favorable upper winds that lie ahead... and increase in computer model support showing development. In this update I have not opted for a tropical cyclone formation forecast (with specific track and intensity points) or odds higher than 80% as shear will not be totally absent due to this system's track keeping it on the south side of the Caribbean upper ridge where northerly shear may reduce the system's northern outflow or keep the thunderstorm activity pushed toward the south side of the center of rotation.
Regardless of tropical cyclone formation or not in the short-term...heavy rainfall and gusty winds for the southern Lesser Antilles... Trinidad and Tobago... and northeastern Venezuela are expected over the next 24 hours. If this system track further to the south... or if northerly shear pushes the thunderstorm activity associated with this system sufficiently southward... heavy rains and gusty winds are also possible for northwestern Venezuela... the ABC Islands (Aruba Bonaire and Curacao)... and the Guajira peninsula of northern Colombia on Thursday through early Friday. I recommend interests in Nicaragua should continue to 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 (0000Z Oct 6)...80% chance of tropical cyclone formation (just west of the southern Lesser Antilles near 12.2N-62.5W)
IOH 48 Hr Outlook (0000Z Oct 7)...80% chance of tropical cyclone formation (southeastern Caribbean Sea near 13.5N-67.5W)
IOH 72 Hr Outlook (0000Z Oct 8)...80% chance of tropical cyclone formation (central Caribbean Sea near 13.9N-71W)
IOH 96 Hr Outlook (0000Z Oct 9)...80% chance of tropical cyclone formation (central Caribbean Sea near 14N-76W)
IOH 120 Hr Outlook (0000Z Oct 10)...80% chance of tropical cyclone formation (east of northern Nicaragua near 14N-80.5W)
AREA OF INTEREST #36...The surface frontal cyclone parked offshore of the United States mid-Atlantic coast has not developed thunderstorm activity as the cold temperatures of the supporting upper vortex have not been able to kick off instability. Therefore I have dropped odds of subtropical cyclone formation for this feature to 0% in this update. Going forward... the current upper trough over the western Dakotas and another trough diving southeast from western Canada will merge into an amplified upper trough to settle over eastern North America. This trough will jettison the parent upper vortex of the frontal cyclone to the northeast... which will ultimately cause the the vortex to leave behind the frontal cyclone with the cyclone weakening 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 forecast track has a northward adjustment in this update to account for the current position of the frontal cyclone.
The surf being generated along the US mid-Atlantic coastline by the frontal cyclone is expected to relax over the next 24 hours as the cyclone shifts to the east and weakens with time going forward.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Oct 6)...0% chance of subtropical cyclone formation (offshore of southeastern Maryland near 36.2N-73W)
AREA OF INTEREST #37...At the end of September as Hurricane Ian was gradually transitioning into a less tropical system over the Florida peninsula... the eastern divergence zone of the shortwave upper trough interacting with the hurricane at the time generated a frontal-like surface trough of low pressure extending south from Ian. The surface trough has since expanded further south and matured in the western Caribbean... midway between Jamaica and Honduras... while supported by the outflow of a persistent upper ridge axis in the region. The surface trough was also enhanced by split flow upper divergence between the west side of dissipating upper vorticity that approached from the east in recent days and the south side of the upper ridge axis. Over the last day or so the surface trough has generated persistent thunderstorm activity... and I have introduced it as an area of interest for tropical development. This marks the thirty-seventh Atlantic tropical area of interest I have tracked on this blog this year. I assign low 10% odds of tropical cyclone formation as computer models do not develop this feature and it does not have a well-defined area of low-level spin as seen in the CIMSS 850 mb vorticity product (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=). However this system remains in a low shear and upper outflow environment... and it would not surprise me if this system develops a thunderstorm flare that generates a better defined surface tropical low pressure spin or a tropical depression. Surface high pressure ridging over the eastern United States and Gulf of Mexico has been present initially due to the western convergence zone of the shortwave upper trough that interacted with Ian a few days ago... and as of late due to the western convergence zone of the current eastern US upper vortex. The western convergence zone of a major upper trough to develop and settle over eastern North America will also continue this surface ridging in the days ahead. This ridging has prevented this system from moving northwest toward the Gulf of Mexico... and anything that does develop is likely to drift west-southwest into Honduras over the next couple of days.
This system may produce heavy rainfall for Honduras and northern Nicaragua in the days ahead... which will only add to rainfall totals in the region out ahead of area of interest #35 which will be approaching from the east by this weekend. Should this occur...the combined rainfall totals from this system and eventually area of interest #35 could become excessive.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Oct 6)...10% chance of tropical cyclone formation (just offshore of northeastern Honduras near 16N-84W)
IOH 48 Hr Outlook (0000Z Oct 7)...10% chance of tropical cyclone formation (northeast coast of Honduras near 15.8N-85W)
IOH 72 Hr Outlook (0000Z Oct 8)...0% chance of tropical cyclone formation (north-central Honduras near 15.2N-86.2W)
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)
1200Z (Oct 4) CMC Model Run...
**For Tropical Depression Twelve... weakens to a trough near 16.5N-35W at 42 hours.
**For area of interest #35... tropical cyclone formation suggested just offshore of the Guajira peninsula of northern Colombia at 72 hours... acquires hurricane strength near 13.5N-78.5W at 102 hours... makes landfall on the northeast coast of Nicaragua at 132 hours.
**For area of interest #36... frontal cyclone currently offshore of Maryland shifts east while weakening and dissipates near 36N-70W at 48 hours.
**For area of interest #37... no development shown
1200Z (Oct 4) ECMWF Model Run...
**For Tropical Depression Twelve... weakens to a trough near 22.5N-39.8W at 72 hours... remnant trough continues west-northwest and re-gains tropical depression status near 28.5N-55W at 144 hours
**For area of interest #35... tropical cyclone formation suggested near 14N-78.5W at 96 hours... makes landfall on the central coast of Nicaragua at 120 hours as a strengthening tropical storm.
**For area of interest #36... frontal cyclone currently offshore of Maryland shifts east while weakening and dissipates near 35.5N-70W by 48 hours.
**For area of interest #37... no development shown
1800Z (Oct 4) GFS Model Run...
**For Tropical Depression Twelve... weakens to a trough near 23N-35.5W at 48 hours.
**For area of interest #35... tropical wave evolves into broad central Caribbean disturbance with two areas of rotation (one near 15N-74.5W and another near 11N-80.5W) through 120 hours... the larger northeastern rotation absorbs the smaller southwestern one and becomes a tropical cyclone near 15N-77W at 138 hours.
**For area of interest #36... frontal cyclone currently offshore of Maryland shifts east while weakening and dissipates near 36N-70W at 42 hours.
**For area of interest #37... no development shown
1800Z (Oct 4) NAVGEM Model Run...
**For Tropical Depression Twelve... weakens to a trough near 21.5N-41.2W at 78 hours... remnant trough continues west-northwest and re-gains tropical depression status near 26.2N-55.5W at 120 hours
**For area of interest #35... tropical cyclone formation suggested near 14.5N-72.5W at 72 hours... located east of the Nicaragua/Honduras border as a potentially intense tropical cyclone near 15.5N-80.5W at 120 hours.
**For area of interest #36... frontal cyclone currently offshore of Maryland shifts east while weakening and dissipates near 36.2N-73.5W at 30 hours.
**For area of interest #37... no development shown