*******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 11 2023 1:52 PM EDT...
For the eastern Atlantic Ocean... the deep-layer cyclone north of the Azores has not developed tropical characteristics... and is not expected to do so going forward... see area of interest #43 section below for more details. Further south and in the tropical latitudes... the western of the two vigorous tropical waves of low pressure has become Tropical Storm Sean while the eastern of the two has been added into the NHC tropical weather outlook within the last 36 hours and continues to be monitored for signs of tropical cyclone formation. See Sean and Area of Interest #45 sections below for more information on both systems.
For the central Atlantic Ocean... a portion of the eastern North America upper vortex has ejected toward the mid-latitude regions of the open central Atlantic. The divergence zone of this upper trough is producing a new frontal low near 36N-54W as of 0600Z this morning. The latest model runs indicate that the remainder of the eastern North America upper vortex will soon shift offshore and become entangled with the upper trough such that the trough has a lower amplitude featuring excess wind shear and less upper divergence... making it less likely the new frontal low acquires tropical characteristics. Therefore the new frontal low is not being considered a tropical area of interest.
For the Gulf of Mexico... the troipcal disturbance in the region has transitioned into an elongating non-tropical frontal low pressure bringing heavy rainfall to the southeastern United States... see area of interest #46 section below for an update.
For the northwestern Caribbean Sea... the remnant frontal low pressure of the Gulf of Mexico disturbance and currently developing frontal low over the western US will work together to drive the tail end of a surface cold front into the region by day 7. Meanwhile some model runs indicate that enough tropical upper ridging with low shear and outflow may persist over the region through that time to potentially convert the tail end of the front into a tropical disturbance... as such another tropical area of interest may emerge in the northwestern Caribbean Sea within the next seven days.
TROPICAL STORM SEAN... The western of the two active tropical waves of low pressure in the eastern tropical Atlantic finally became tropical depression nineteen at 11 PM EDT last evening and then Tropical Storm Sean by 5 AM EDT this morning. Meanwhile see area of interest (AOI) #45 section below for an update on the eastern of the two waves. The delayed development of this system into Sean may have been due to competition for surface inflow and upper ouflow with AOI #45... with Sean perhaps finally coming into existence as AOI #45 has not moved as fast to the west such that Sean and AOI #45 are now far enough away from each other to stop interfering with each other. The forecast track for Sean is shifted more westward and less northward due to the current position of the storm relative to the previous forecast... and as the current eastern Atlantic surface ridge is slated to remain intact and expand westward as the latest eastern Atlantic upper trough has merged with a lingering central Atlantic upper vorticity string to make a lengthy southwest-northeast upper vorticity axis... with upper convergence on the back (northwest) side of the upper vorticity string and southeast side of the ongoing central Atlantic upper ridge helping the eastern Atlantic surface ridge. My updated forecast track takes Sean into increasingly stronger southwesterly shear through 48 hours as it nears the upper vorticity axis... upon which time I forecast Sean to dissipate into a remnant low. By 72 hours my updated track takes Sean directly below the upper vorticity axis where a lack of upper divergence would keep Sean supressed. Recent global models runs more or less agree on keeping Sean a weak system or dissipate it except the NAVGEM which actually strengthens Sean by keeping the storm's westward track north enough such that it finds a break in the upper vorticity axis as the upper vorticity begins to weaken and split into two upper vortices at 72+ hours (the upper vorticity indeed does weaken while remaining cut-off from high-latitude cold air).
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0600Z Oct 11)... 40 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 10.3N-33.1W
IOH 24 Hr Forecast (0600Z Oct 12)... 35 mph maximum sustained wind tropical depression centered in the eastern tropical Atlantic at 11.5N-37.5W
IOH 48 Hr Forecast (0600Z Oct 13)... Remnant low centered in the central tropical Atlantic at 12.5N-41W
******National Hurricane Center (hurricanes.gov) official forecast as of 11 AM EDT***************************
Peak Strength (1200Z Oct 12)... 45 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 11.7N-37.4W
Loss of Tropical Cyclone Status (1200Z Oct 16)... 35 mph maximum sustained wind remnant low centered in the central tropical Atlantic at 18.1N-48.9W
AREA OF INTEREST #43... A deep-layer cyclone persists north of the Azores consisting of a surface low stacked below its parent upper vortex. The system as a whole has been dragged east over the last 36 hours by a high-latitude upper trough that has moved from Greenland to the northeast corner of the Atlantic. Due to the force of the adjacent upper ridge to the west... the upper vortex has become oblong in a southwest-to-northeast orientation... with the surface low bending northeastward in track while whirling toward the northeast half of the upper vortex. This track has moved the surface low into cooler waters below 20 deg C... near 43N-27.5W as of 0600Z today... which has contributed to reducing the core shower and thunderstorm activity. As such the surface low has lost its opportunity to become a subtropical cyclone. Going forward the upper vortex shifts east while dragged by the next high-latitude upper trough to approach from Greenland... with the surface low continuing to weaken while remaining below a lack of divergence below the core of the upper vortex. Over the next 24 hours the surface low is expected to make a small cyclonic loop beneath the eastward-shifting upper vortex... keeping it over the same place or perhaps a little west of its current position. By 48 hours the surface low is likely to dissipate while shifting southeastward in the suppressing upper convergent northwesterly flow on the back side of the eastward-shifting upper vortex.
Any coastal surf for the Azores being generated by this system should fade over the next 48 hours as the surface low continues to weaken... this is my final statement on this area of interest on this blog as its subtropical development is no longer possible.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Oct 12)... 0% chance of subtropical cyclone formation (northeast Atlantic near 43N-28.5W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT***************************
Not in the official outlook
AREA OF INTEREST #45... The tropical wave of low pressure that emerged into the eastern tropical Atlantic from Africa... behind what is now Tropical Storm Sean... slowed down its westward progress perhaps as the eastern Atlantic surface ridge was weakened to the southwest of the Canary Islands by the divergence zone of the latest eastern Atlantic upper trough. As discussed in the Sean section above... this upper trough is merging with lingering central Atlantic upper vorticity to make a lenghty southwest-northeast upper vorticity axis... with convergence on the back (northwest) side of the axis and southeast side of the ongoing central Atlantic upper ridge ensuring that the eastern Atlantic surface ridge will make a recovery and send this tropical wave back on a faster westward track. My updated forecast track below reflects the current position of the tropical wave and above thinking... albeit I have some northward slant to the track from 24 to 72 hours as this system potentially becomes stronger/taller to couple with upper winds and hence potentially becomes dragged by the flow ahead of the aforementioned upper vorticity axis. After 72 hours the upper vorticity string weakens and splits into a pair of upper vortices while remaining cut-off from high-latitude cold air... thus I show a more westward track as the upper vorticity string loses its influence even if this system were to become stronger/taller.
Regarding odds of tropical cyclone formation... overall they appear higher than my last update as the increased distance between this system and Sean has ended Sean's potential to absorb this system. Due to this system's current organization on satellite pictures and I have raised short-term odds of cyclone formation to 40%. From 48 to 96 hours this system is at risk of dealing with westerly shear on the north side of the regional tropical upper ridge and out ahead of the upper vorticity axis... thus I lower odds of development to 20%. I begin to pull odds of development back up by day 5 as the upper vorticity axis weakens as discussed above... which would allow this system to find a better lower shear and upper outflow environment between the two remnant upper vortices.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Oct 12)... 40% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-22.5W)
IOH 48 Hr Outlook (0600Z Oct 13)... 20% chance of tropical cyclone formation (south-southwest of the Republic of Cabo Verde Islands near 11.5N-26W)
IOH 72 Hr Outlook (0600Z Oct 14)... 20% chance of tropical cyclone formation (eastern tropical Atlantic near 12.5N-30W)
IOH 96 Hr Outlook (0600Z Oct 15)... 20% chance of tropical cyclone formation (eastern tropical Atlantic near 13N-35W)
IOH 120 Hr OUtlook (0600Z Oct 16)... 30% chance of tropical cyclone formation (central tropical Atlantic near 13.5N-40W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT***************************
Formation chance through 48 hours... 20%
Formation chance through 7 days... 30%
AREA OF INTEREST #46... The tropical low pressure in the western Gulf of Mexico has spent the last 36 hours lifting northward in the flow ahead of eastern Pacific tropical cyclones Lidia and Max which made landfall in south-central central Mexico. Aircraft recon yesterday afternoon investigated the tropical low pressure and found it had too elongated of a circulation to declare a tropical cyclone. The elongated structure continues with a comma-shaped thunderstorm mass in infrared colorized satellite pictures suggesting a center near 25N-94W as of 1200Z today... but true-color visible satellite animation showing an oblong circulation reaching as far west as 96W. In fact the NHC TAFB surface analysis suggests the lowest surface pressure is toward the west and well-removed from the comma-shaped thunderstorm mass. This system is interacting with a complex upper trough over western North America which features a southwest-to-northeast tilted leading piece of energy over northwestern Mexico and western Texas and northwest-to-southeast tilted trailing piece of energy now making landfall over the northwestern US and Canada. The elongating structure of this system suggests it is now transitioning into a non-tropical frontal low supported by the elongated divergence zone ahead of the leading piece of energy... with the frontal low separating cold air associated with the energy and warm air ahead of the energy. Models continue to suggest the elongating remnant circulation splitting in half... with the eastern half zooming across north Florida and western Atlantic as part of the leading upper trough energy becomes an eastward-zooming shortwave upper trough... and with the western half becoming another frontal low lifting northeastward across the southeastern US and eventually the coastal regions of the Carolinas while supported by the divergence zone of the trailing upper trough energy.
Even though this system no longer poses a threat of tropical cyclone formation... it will still bring impacts to a large swath of the southeastern US in the form of heavy rainfall over the next couple of days. Radar shows heavy rain has already developed across far eastern Texas... Louisiana... Mississippi... Alabama...
the Florida panhandle... and Georgia. The heavy rainfall is expected to pivot across the remainder of Florida... the Carolinas... and eastern Tennessee.
The NHC has removed this system from their tropical weather outlook as it has transitioned into an elongating non-tropical frontal low pressure area... and this is also my final statement on this area of interest on this blog.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0600Z Oct 12)... 0% chance of tropical cyclone formation (just offshore of southeastern Louisiana near 28.5N-90W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 AM EDT***************************
Not in the official outlook
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields(http://moe.met.fsu.edu/tcgengifs/).
0000Z (Oct 11) CMC Model Run...
**For Tropical Storm Sean... stays a weak tropical cyclone while moving west-northwest to 19N-46.5W through 120 hours
**For area of interest #43... surface low north of the Azores dissipates near 41N-26W at 54 hours
**For area of interest #45... no development shown for tropical wave currently just offshore of the west coast of Africa
**For area of interest #46... transitions into an elongating frontal low that makes landfall over the central Florida panhandle coast at 42 hours... through 90 hours the remnant frontal low drits northeastward inot coastal South Carolina where it is absorbed by another larger frontal low that pivots into the eastern US from its initial western US position.
**Frontal low develops over the western US at 30 hours after which time it moves into the eastern US and offshore western Atlantic waters through 120 hours as the tail end of its cold front arrives into the northwestern Caribbean Sea... tail end of front evolves into a tropical low just offshore of northeastern Honduras through 168 hours
0000Z (Oct 11) ECMWF Model Run...
**For Tropical Storm Sean... stays a weak tropical cyclone and then dissipates near 19.5N-48.5W at 108 hours
**For area of interest #43... surface low north of the Azores dissipates near 42.5N-25W at 42 hours
**For area of interest #45... no development shown for tropical wave currently just offshore of the west coast of Africa
**For area of interest #46... transitions into an elongating frontal low just offshore of southeastern Louisiana through 24 hours... dissipates while moving into northern Florida while additional elongating frontal low forms just to its east and offshore of the southeastern US
0000Z (Oct 11) GFS Model Run...
**For Tropical Storm Sean... stays a weak tropical cyclone and then weakens to a remnant low near 14.5N-41.5W at 87 hours... remnant low weakens further to a remnant tropical wave near 15N-48W through 120 hours
**For area of Interest #43... surface low north of the Azores dissipates near 40.8N-25.5W at 57 hours
**For area of interest #45... no development shown for tropical wave currently just offshore of the west coast of Africa
**For area of interest #46... transitions into an elongating frontal low just offshore of southeastern Louisiana through 24 hours... makes landfall on the Florida panhandle at 66 hours and then becomes an intensifying frontal low that slides along the southeastern US coast from Georgia to the Carolinas through 93 hours... frontal low intensifies into a frontal cyclone that continues northeastward and offshore and reaches 38.5N-60W through 120 hours.
0000Z (Oct 11) NAVGEM Model Run...
**For Tropical Storm Sean... strengthens into a hurricane that moves west-northwest to 20N-45W through 120 hours
**For Area of Interest #43... surface low north of the Azores dissipates near 41N-25W at 48 hours
**For area of interest #45... no development shown for tropical wave currently just offshore of the west coast of Africa
**For area of interest #46... transitions into an elongating frontal low that makes landfall over southeastern Louisiana through 30 hours... moves east-northeast across the southeastern US and then begins to intensify offshore of the Carolinas at 90 hours... frontal low passes just north of Bermuda through 120 hours shortly after which time it becomes absorbed by frontal cyclone that develops to the northeast (the adjacent frontal cyclone develops with support of upper vortex over eastern North America when that vortex later moves offshore)
**Tropical wave emerges from west coast of Africa at 78 hours and organizes into a tropical low near 10.5N-28W by 168 hours