*******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.**********
...THURSDAY OCTOBER 17 2019 1:28 PM EDT...
See area of interest sections below for all areas being monitored for tropical and subtropical cyclone formation...in particular area of interest #1 which is at risk for producing heavy rainfall...wind...and some coastal sea swells to parts of the southeastern United States by 48 hours regardless of whether this area of interest acquries tropical characteristics. Elsewhere...the remnant surface trough of low pressure of tropical depression fifteen well west-northwest of the Republic of Cabo Verde Islands is reproducing thunderstorms...but this activity is dislodged well north of the maximum spin seen near 20N-31W due to southwesterly wind shear from a cut-off upper trough in the region. Tropical cyclone reformation is not expected here as the shearing cut-off upper trough gets re-enforced by upper vorticity from the current upper trough approaching from the northwestern Atlantic.
AREA OF INTEREST #1...The developing surface low pressure that has emerged into the western Gulf of Mexico from the Bay of Camepche continues shifting north as it transitions into a system supported by the eastern divergence zone of a Texas cut-off upper trough left behind by the northeastern US frontal cyclonic system. The result is this surface low pressure and its expansive area of thunderstorms are supported by both tropical and non-tropical processes...the tropical part being the tremendous latent heat release of the thunderstorms bolstering the Gulf of Mexico upper ridge to the south...with that ridge helping the upper outflow of the surface low pressure...and the non-tropical part being the aforementioned support of the Texas cut-off upper trough. Although the National Hurricane Center (NHC) has now classified the low pressure as potential tropical cyclone sixteen to allow for tropical storm warnings to go up on parts of the northern US Gulf coast...their 1200Z surface analysis also has the low pressure along the cold front extending from the northeastern US frontal cyclone...therefore instead of doing a tropical or subtropical cyclone formation forecast...I am maintaining my short-term 70% odds of acquisiton of tropical characteristics as I am not absolutely certain if the National Hurricane Center will later classify this system as having such characteristics. I have added the phrase "tropical or subtropical" in the updated outlook below as I am also unsure which classification the National Hurricane Center will go with in the event they do consider the low pressure as having tropical characteristics. Regardless for the next 48 hours...this surface low pressure will be vigorous enough to bring heavy rainfall...possible sea swells...and gusty and possibly damaging wind to coastal Alabama...northern Florida...and southern Georgia. My updated forecast track is nudged northward to account for the 11 AM EDT NHC forecast track and more northward position in the 0600Z GFS model run...but I am not convinced just yet of this system being quiet as far north as shown in the 0600Z GFS as a look at the same model's upper-level wind field shows to me the maximum upper divergence zone of the cut-off upper trough emerging from Texas being further south in the next 72 hours. However I am now considering southern and coastal South Carolina...as well as southeastern North Carolina...also at risk of similar impacts. By 96 to 120 hours...as this system settles on the west side of the fast-moving surface ridge currently over the central US...the ridge appears it will block this system from moving eastward out to sea...likely bending the track of this system northward parallel to the eastern US coast. And durng this time as the cut-off upper trough shifts southeastward and away while warm core upper ridging builds overhead in warm air advection ahead of two strong frontal lows forecast to eject from the western US into Canada during the forecast period...I drop the odds of tropical or subtropcial cyclone formation at 120 hours due to cooler waters. My 72 and 96 hour forecast points meanwhile are raised from 50% to 60% as my northward adjusted track increases the odds of the circulation center moving over warm Gulf stream waters instead of straddling either side of the stream...with odds briefly dipped to 50% at 48 hours to account for likely land interaction with northern Florida.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Oulook (1200Z Oct 18)...70% chance of tropical or subtropical cyclone formation (central Gulf of Mexico near 25.7N-90W)
IOH 48 Hr Outlook (1200Z Oct 19)...50% chance of tropical or subtropical cyclone formation (northern Florida near 30N-82.5W)
IOH 72 Hr Outlook (1200Z Oct 20)...60% chance of tropical or subtropical cyclone formation (just offshore of the North Carolina coast near 33N-75.5W)
IOH 96 Hr Outlook (1200Z Oct 21)...60% chance of tropical or subtropical cyclone formation (offshore of the northeastern United States coast near 36.5N-71W)
IOH 120 Hr Outlook (1200Z Oct 22)...20% chance of tropical or subtropical cyclone formation (just south of Cape Cod Massachusetts near 40N-70W)
AREA OF INTEREST #2...The tropical wave in the central Atlantic just east of the Lesser Antilles is seeing a notable increase in thunderstorm bands while interacting with the eastern divergence zone of a sharp upper trough over the Lesser Antilles soon to be cut-off from its parent upper trough over the northwest Atlantic by amplfiying Gulf of Mexico upper ridging. I have generally maintained my previous odds of tropical cyclone formation...and will only increase them should the thunderstorm activity organize and/or computer model support develops. Because the upper trough will be sharp in nature...this will keep wind shear low should a disturbance emerge in the current activity...which could aid in short-term tropical development. The upper trough will also likely curve any such disturbance northward. In addition a northward turn would be induced in the low-levels as the northeastern US frontal cyclone creates a surface ridge weakness while moving into the western Atlantic. By 48 hours...the surface ridge weakness begins closing...which would begin a westward turn of any disturbance that develops. The GFS continues to show an area of upper anticyclonic flow overspreading the region out ahead of the cut-off upper trough supporting area of interest #1...thus I continue to climb odds of development through 72 hours. But later as the cut-off upper trough from area of interest #1 seperates from that area of interest and settles over this disturbance by 96 to 120 hours...it could either disrupt the disturbance which is why I lower odds of development by then...or alternatively re-energize the disturbance with its eastern divergence zone...and in a low shear environment as this cut-off upper trough too is shown in the latest GFS to be sharp in nature as well. Due to uncertainty with how this disturbance would interact with this cut-off upper trough...my 96 and 120 hour forecast positions for now are the same.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Oulook (1200Z Oct 18)...0% chance of tropical cyclone formation (just east of the northern Lesser Antilles near 18.5N-59.2W)
IOH 48 Hr Oulook (1200Z Oct 19)...10% chance of tropical cyclone formation (just northeast of the northern Lesser Antilles near 21.1N-61W)
IOH 72 Hr Oulook (1200Z Oct 20)...20% chance of tropical cyclone formation (north of Puerto Rico near 22.5N-64W)
IOH 96 Hr Oulook (1200Z Oct 21)...15% chance of tropical cyclone formation (western Atlantic near 23.5N-67W)
IOH 120 Hr Outlook (1200Z Oct 22)...5% chance of tropical cyclone formation (western Atlantic near 23.5N-67W)