MY 2019 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #170
*******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.**********
...MONDAY OCTOBER 28 2019 4:21 PM EDT...
Hurricane Pablo has rapidly weakened and lost tropical characteristics over the cold waters southwest of the British Isles...see remnants of Pablo section below for more details. See area of interest section below for details on the hurricane-force non-tropical cyclone in the northwest Atlantic currently being monitored for acquisition of tropical characteristics. Elsewhere...the north end of a passing tropical wave and tail end of a lingering surface front in the Gulf of Mexico are combining to produce a surface trough of low pressure with loosely-packed thunderstorm cells. So far this system is not organized enough to be considered at risk of tropical development...and will only have 72 hours to tropically develop further before a rapidly strengthening frontal cyclone over the central United States dominates the Gulf of Mexico with a cold front (this frontal cyclone is forecast to form with the support of a lobe of vorticity swinging around the south side of the larger central Canadian upper vortex currently present).
REMNANTS OF PABLO...At last while moving over even cooler northeastern Atlantic waters southwest of the British Isles...Pablo loses thunderstorm activity and its warm core to be classified as a tropical cyclone. The remnant circulation is now a frontal cyclone that will soon lose its identity to the much larger and more powerful frontal cyclone mentioned in the area of interest #1 section below and located to the southwest. This is my final statement on Pablo as it is no longer a tropical feature.
AREA OF INTEREST #1...The cold air advection (southward cold air transport) on the west hurricane-force frontal cyclone in northwestern Atlantic has amplified the south part of its supporting upper trough into an upper vortex...and the frontal cyclone in turn has whirled beneath the center of the new upper vortex at a location of 42.5N-40W. Going forward...this storm will undergo classical post-mature slow decay as a frontal cyclone due to a lack of upper divergence at the center of the upper vortex. The question remains as to whether or not the core of this decaying storm will acquire tropical characteristics while moving over 18 to 20 deg C waters over the next few days. Cold upper air temperatures of the upper vortex may allow for thunderstorms to develop despite the mild water temperatures...and indeed this storm system has a similar thermodynamic profile to the recent Hurricane Pablo that formed in similar circumstances. Even though a core of thunderstorms has not developed thus far...I have kept my odds of subtropical cyclone formation at 50% as the National Hurricane Center has now introduced this system into their tropical weather outlook. There has been a change in how the computer models handle this storm...and it appears to lie with the evolution of the central Canadian frontal cyclone. Previous model runs had the upper vortex stretching into a southwest-northeast elongation due to the warm upper ridging to the west driven by the warm sector of the Canadian cyclone...with the vortex then opening into a trough and kicked northeastward when the upper trough energy of the Candian frontal cyclone finally shifts eastward toward this storm system. While the models still show this generally occurring...in the short term there now appears to be enough upper ridging in the higher (more northern) latitudes within the eastern warm sector of the Canadian cyclone such that the elongating upper vortex now splits in half...with the southern half keeping this storm system at a further south location...and the north half producing yet another frontal cyclone to the northeast. Therefore my updated forecast track in the outlook below is adjusted southward...but still shows an eastward acceleration later on when both split halves of the upper vorticity are expected to shift eastward. I drop the odds of subtropical cyclone formation to 0% by 96 hours as this storm system will likely be rapidly weakening while falling behind the eastward-accelerating upper vorticity...leaving the storm in unfavorable western convergence on the west side of the upper vorticity. Given the updated more south forecast track...interests in the Azores can expect a round of coastal sea swells and possible gusty winds from now till Thursday. The gusty winds in the near-term would be from the large size of the strong storm circulation despite being centered well west of the islands...and in the longer range would be from the circulation nearing the islands despite the storm circulation gradually weakening and shrinking.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Oct 29)...50% chance of subtropical cyclone formation (central Atlantic near 42.5N-40W)
IOH 48 Hr Outlook (1800Z Oct 30)...50% chance of subtropical cyclone formation (central Atlantic near 42.5N-40W)
IOH 72 Hr Outlook (1800Z Oct 31)...50% chance of subtropical cyclone formation (central Atlantic near 42.5N-35W)
IOH 96 Hr Outlook (1800Z Nov 1)...0% chance of subtropical cyclone formation (just north of the Azores near 42.5N-27W)