*******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.**********
...SATURDAY OCTOBER 5 2019 3:37 PM EDT...
See area of interest sections below for areas being monitored for tropical and subtropical cyclone formation. Elsewhere...the showers and thunderstorms in the northwestern Caribbean Sea that have persisted under the outflow of an upper ridge cell in the area have developed a surface trough of low pressure. However...computer model support showing tropical development is not present...and conditions for development will become less favorable by 3 days as southwesterly shear increases from the upper trough currently over western North America. Regardless of development...the eastern upper divergence zone of this upper trough could cause the moisture from this disturbance to spread northward from western Cuba and the Cayman Islands into the Florida peninsula and western Bahamas by 3 days...with flash flooding possible in any heavy persistent rainfall.
AREA OF INTEREST #1...The tropical wave passing south of the Republic of Cabo Verde Islands where it continues to produce showers and thunderstorms. Because its associated activity has not become better organized...I have slightly lowered odds of tropical cyclone development in the short-term. Upper-level winds are currently favorable for tropical development as an expansive upper ridge cell (with low shear and upper outflow) persists over the eastern Atlantic. The rapidly strengthening frontal low in the northwest Atlantic will have no effect on this system while passing too far north...but a rather amplifed upper trough associated with it will strengthen the Atlantic surface subtropical ridge with its western convergence by 48 to 72 hours such that a westward acceleration in track of this disturbance will be possible during those timeframes. I drop the odds back to 0% by 96 hours as lingering central Atlantic upper vorticity is expected to begin negatively shearing this disturbance...especially as it merges with a forecast cut-off upper vortex associated with the disturbance in area of interest #2.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Oct 6)...0% chance of tropical cyclone formation (tropical Atlantic near 30W)
IOH 48 Hr Outlook (1800Z Oct 7)...5% chance of tropical cyclone formation (tropical Atlantic near 36W)
IOH 72 Hr Outlook (1800Z Oct 8)...10% chance of tropical cyclone formation (tropical Atlantic near 42W)
IOH 96 Hr Outlook (1800Z Oct 9)...0% chance of tropical cyclone formation (tropical Atlantic near 47W)
AREA OF INTEREST #2...In their 5-day tropical weather outlook...the National Hurricane Center continues to mention a surface cold front and upper trough which has emerged from the northeastern US into the northwestern Atlantic...because all major computer models (CMC...NAVGEM...Euro...GFS) agree that these features will evolve into a cut-off deep-layered low pressure by 3 to 5 days capable of acquiring tropical characteristics in the open central Atlantic. At the surface...the cut-off is expected to be induced by a strong surface ridge to build in the central Atlantic in 48 to 72 hours due to increasing western convergence of the sharpening upper trough...and the upper trough is expected to sharpen with a portion of the trough becoming a cut-off upper vortex due to broad upper ridging amplifying to the west in warm surface southerly flow ahead of a strong central US/Canada frontal cyclone to form from the sharp upper trough currently over western North America. The surface and upper-level ridging is expected to drive the resulting cut-off deep-layered low pressure west-southwestward by days 3 to 5. Although this feature is expected to form over waters typically too cool for tropical development...the cold temperatures of the cut-off upper vortex are likely to de-stabilize the atmosphere for thunderstorm activity to develop. My 120-hour peak odds of development are been raised to 65% at 96 hours as the GFS has joined with the remaining models in showing the formation of the deep-layered low pressure. I begin dropping the odds of development by 120 hours as the surface ridging will be passing to the north and drive the surface circulation west-southwestward into the less favorable convergent west side of the cut-off upper vortex. My initial forecast track is adjusted southward based on the current position of the most active thunderstorm area along the current cold front in the northwest Atlantic...followed by a westward adjustment in the later part of the forecast as the latest GFS model run depicts the cut-off upper vortex (and resulting surface circulation it will trigger) forming at a location further west.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Oct 6)...0% chance of subtropical cyclone formation (central Atlantic near 32.5N-45W)
IOH 48 Hr Outlook (1800Z Oct 7)...0% chance of subtropical cyclone formation (well southwest of the Azores near 32.5N-35W)
IOH 72 Hr Outlook (1800Z Oct 8)...25% chance of subtropical cyclone formation (central Atlantic near 31N-40W)
IOH 96 Hr Outlook (1800Z Oct 9)...65% chance of subtropical cyclone formation (central Atlantic near 30N-45W)
IOH 120 Hr Outlook (1800Z Oct 10)...50% chance of subtropical cyclone formation (central Atlantic near 29N-50W)
AREA OF INTEREST #3...A swirl of showers and thunderstorms currently north of the Bahamas is associated with a cut-off upper vortex at the present time...and has been introduced into the 5-day National Hurricane Center tropical weather outlook as this disturbance could evolve into a formidable subtropical cyclone just offshore of the northeastern US in about 5 days. This disturbance appears it will initially slowly drift northward or northwestward under the influence of the eastern US/Canada surface ridge as that ridge moves into the western Atlantic...and as the cut-off upper vortex gravitates northwestward toward and eventually merges with the sharp upper trough currently over western North America. The merger should be completed by 48 hours...upon which time a tremendous area of upper divergence on the east side of the merged upper trough as well as outflow of upper ridging to the east could cause some subtropical development by that time (however I only have odds of subtropical cyclone formation at 10% at that timeframe due to lack of computer model support showing a well-defined surface low pressure). By 72 hours...whatever surface low pressure forms from this disturbance will have merged with the cold front of the merged upper trough...making this disturbance lose tropical characteristics. What happens after 72 hours could get quiet interesting at a location northwest of Bermuda and offshore of the eastern US coast...as the CMC...NAVGEM...Euro...and GFS models now all agree a round of amplifying warm deep-layered ridging to the west and north could cut-off the tremendous merged upper trough into a rather impressive upper vortex...with this disturbance perhaps evloving into a large and strong subtropical cyclone whose thunderstorms would be supported by the cold temepratures of the upper vortex depsite being over mild water temperatures. The warm deep-layered ridging during that timeframe looks like it will be induced by plenty of warm air advection ahead of a strong forecast frontal cyclone over central Canada (currently the energy for this forecast frontal cyclone lies with an upper vortex over Alaska). My 120-hour odds of subtropical cyclone formation are 35% due to the strong computer model agreement...and I plan to raise them in my next update if the model consensus continues.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Oct 6)...0% chance of subtropical cyclone formation (northeast of the eastern Bahamas near 26N-69W)
IOH 48 Hr Outlook (1800Z Oct 7)...10% chance of subtropical cyclone formation (western Atlantic near 29N-69.5W)
IOH 72 Hr Outlook (1800Z Oct 8)...0% chance of subtropical cyclone formation (western Atlantic near 35N-70W)
IOH 96 Hr Outlook (1800Z Oct 9)...0% chance of subtropical cyclone formation (western Atlantic offshore of the northeastern US coast near 37.5N-67.5W)
IOH 120 Hr Outlook (1800Z Oct 10)...35% chance of subtropical cyclone formation (south of Cape Cod Massachusetts near 37.5N-70W)