*******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.*********
...THURSDAY OCTOBER 12 2023 11:43 PM EDT...
For the eastern tropical Atlantic Ocean... Tropical Storm Sean is expected to weaken due to unfavorable upper winds in the short-term... but could find more favorable upper winds in the long-term... see Sean section below for more information. To the east of Sean... monitoring a tropical wave of low pressure following behind which could also take advantage of more favorable upper winds in the long-term... see area of interest #45 section below for more information.
For the central Atlantic Ocean... a frontal low pressure that was located near 36N-48.5W as of 1800Z this evening was producing some intermittent shower and thunderstorm activity at the core of its circulation. However this activity has not persisted enough to mark this system as a tropical area of interest. This system is moving slower to the east than its parent upper trough which will result in it becoming aligned with the suppressive western convergence zone of the trough... therefore the frontal low is expected to weaken and then dissipate going forward.
For the northwestern Caribbean Sea... the frontal cyclone currently over the western US will drive the tail end of a surface cold front into the region by day 6. 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 six days.
TROPICAL STORM SEAN... Sean's westward track has angled more northward over the last several hours while moreso gravitated to the surface ridge weakness associated with the current central Atlantic frontal low than previously forecasted... and the updated forecast track below is adjsuted accordingly. The tropical storm has struggled with southwesterly shear imparted by the nearby string of upper vorticity that has been displacing the thunderstorms northeast of the storm's swirl center... and within the last 24 hours there was a time Sean dipped into weaker tropical depression status. Over the next 24 hours the current heading and forecast track of Sean takes it directly below the axis of upper vorticity where a lack of divergence should suppress Sean... followed by arrival below the even more oppressive upper convergence zone between the back northwestern side of the upper vorticity axis and southeast side of the central Atlantic upper ridge. Thus I continue to forecast Sean to dissipate into a remnant low soon. Noting in the long range the central Atlantic warm core upper ridge is forecast to amplify in warm southerly flow ahead of what is now the frontal cyclone over western North America as that frontal cyclone later moves into the Atlantic. The eastern Atlantic surface ridge is forecast to retrograde westward while aligning with the southeastern convergence zone of the amplifying upper ridge... resulting in a deep-layer ridge. Eventually what is left of Sean will be turned more westward across the open central Atlantic by the deep-layer ridge... with low shear and outflow in the upper layers of the ridge potentially aiding Sean's remnants. So even though Sean could dissipate in the short-term... whatever is left of Sean may need to be watched in the long term.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (0000Z Oct 13)... 40 mph maximum sustained wind tropical storm centered in the eastern tropical Atlantic at 13.8N-38.2W
IOH 24 Hr Forecast (0000Z Oct 14)... Remnant low centered in the central tropical Atlantic at 15.5N-42.5W
******National Hurricane Center (hurricanes.gov) official forecast as of 5 PM EDT***************************
Loss of Tropical Cyclone Status (0600Z Oct 15)... 30 mph maximum sustained wind remnant low centered in the central tropical Atlantic at 19N-44.8W
AREA OF INTEREST #45... The eastern Atlantic tropical wave of low pressure following behind Tropical Storm Sean has become less organized over the last several hours while becoming increasingly sheared by a string of upper vorticity in the region. Going forward a central Atlantic deep-layer ridge is expected to materialize as discussed in the above Tropical Storm Sean section... and at the same time the cool core upper vorticity string is expected to weaken into two upper vortices while remaining isolated from high-latitude cold air. This tropical wave and the pair of upper vortices will continue westward in tandem while pushed around by the deep-layer ridge. This outlook means the wave will be in a potentially more conducive upper air envrionment over time while parked in low shear and upper outflow between the pair of upper vortices... with the inflow into the vortices potentially enhancing the eastern and western outflow of the tropical wave. I agree with the NHC outlook as of this writing which has a lowered 10% odds of tropical cyclone formation in the short-term to acknowledges the short-term disruption in organiziation caused by shear... and also agree with the raised 50% odds of development for the long-range given the long-term more favorable upper wind outlook.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Oct 14)... 10% chance of tropical cyclone formation (eastern tropical Atlantic near 10N-29.5W)
IOH 48 Hr Outlook (0000Z Oct 15)... 30% chance of tropical cyclone formation (eastern tropical Atlantic near 10.5N-34.5W)
IOH 72 Hr OUtlook (0000Z Oct 16)... 50% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-39.5W)
IOH 96 Hr Outlook (0000Z Oct 17)... 50% chance of tropical cyclone formation (central tropical Atlantic near 11.5N-44.5W)
IOH 120 Hr Outlook (0000Z Oct 18)... 50% chance of tropical cyclone formation (central tropical Atlantic near 12N-49.5W)
******National Hurricane Center (hurricanes.gov) official outlook as of 8 PM EDT***************************
Formation chance through 48 hours... 10%
Formation chance through 7 days... 50%
...COMPUTER MODEL SUMMARY...
Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields(http://moe.met.fsu.edu/tcgengifs/).
1200Z (Oct 12) CMC Model Run...
**For Tropical Storm Sean... weakens to a remnant low near 15.5N-44W at 36 hours... remnant low dissipates near 21N-48.5W at 84 hours
**For area of interest #45... tropical cyclone formation suggested near 12N-39.5W at 102 hours... while strengthening into a tropical storm reaches 13.5N-43W at 120 hours
1200Z (Oct 12) ECMWF Model Run...
**For Tropical Storm Sean... weakens to a remnant low near 15N-41W at 24 hours... remnant low dissipates near 19.8N-45W at 66 hours
**For area of interest #45... tropical cyclone formation suggested near 12N-39W at 102 hours... while strengthening into a tropical storm reaches 12.5N-41.5W at 120 hours
1800Z (Oct 12) GFS Model Run...
**For Tropical Storm Sean... weakens to a remnant low near 15.5N-41W at 30 hours... remnant low dissipates near 20.5N-46W at 78 hours
**For area of interest #45... no development shown
**Frontal low currently over western US drives tail end of cold front into the northwestern Caribbean Sea through 84 hours... tail end of front gradually evolves into a tropical low offshore of northern Honduras and near 17N-84W by 153 hours... tropical low drifts west toward the Belize/Mexico border through 168 hours
1800Z (Oct 12) NAVGEM Model Run...
**For Tropical Storm Sean... strengthens into a hurricane that moves west-northwest to 22.5N-52.5W through 120 hours
**For area of interest #45... no development shown