MY 2019 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #169
*******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.**********
...SUNDAY OCTOBER 27 2019 3:28 PM EDT...
See Hurricane Pablo section below for the only active tropical cyclone in the Atlantic basin. See area of interest section below for details on the rapidly developing storm in the northwest Atlantic.Elsewhere...the intersection of a tropical wave from the western Caribbean...a cold front driven by the remnant circulation of Olga...and the outflow of an upper ridge axis in the region have not produced a tropical disturbance over the northern Yucatan peninsula and southern Gulf of Mexico at the present time. Will continue to watch for the development of thunderstorms in this region.
HURRICANE PABLO...Truly remarkable...Pablo has become a hurricane in cool 18 deg C northeastern Atlantic waters while continuing to be slung northward by the larger frontal cyclone surrounding it...and the new frontal cyclone to the west discussed in the area of interest #1 section below. First...I wasn't expecting Pablo to strengthen due to increasing shear as the overhead upper trough de-amplifies while abosrbed by the upper trough of area of interest #1. Perhaps then Pablo is a rather shallow hurricane where its surface circulation and warm core upper outflow are tucked beneath the overhead upper trough...one recent analogue that comes to mind is Hurricane Michael when it attained category 3 instensity on September 5 2012 despite being under a jet of upper westerly winds...with Michael taking advantage of the divergence in the upper jet...and like Pablo was born as a shallow tropical structure in the midst of non-tropical processes. Thus Pablo's thunderstorms likely strengthened in the upper divergence zone on the east side of the overhead upper trough...and like Michael is too shallow to be sheared by the upper winds. What has also taken me by surprise is Pablo is over 18 deg C waters...the most recent example of a similar type of hurricane in this region I can think of is Hurricane Alex in January 2016 which developed over 20 deg C waters...but unlike Pablo lost tropical characteristics once it moved over waters below 20 deg C. Going forward...wind shear will lessen as Pablo moves into deep-layer warm ridging to the north caused by the warm sector of area of interest #1...and this ridging may impart a westward angle in Pablo's northward track. The 24 hour forecast point is over 14 deg C water...so in my updated forecast I assume Pablo will have lost thunderstorms and tropical characteristics by then. We shall see.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Oct 27)...75 mph maximum sustained wind hurricane centered northeast of the Azores at 42.8N-18.3W
24 Hr Forecast (1800Z Oct 28)...Frontal cyclone centered in the northeastern Atlantic at 49N-19W
AREA OF INTEREST #1...A strong hurricane-force frontal cyclone has explosively formed along the surface cold front in northwestern Atlantic in the last 24 hours...but this event has been well forecast by the computer models over the last few days. The genesis of this storm has been from an impressive upper divergence zone on the east side of the front's quickly amplifying upper trough. This has been in response to amplification of upper ridging over eastern Canada in the warm sector of a strong frontal cyclone currently heading into the Hudson Bay region of central Canada. The amplification of the upper trough will result in the formation of a large cut-off upper vortex...and the forecast positions of this storm shown in the outlook below are based on the location of the upper vortex center shown in today's 1200Z GFS model run...which is essentially the same as yesterday's runs. However my short-term forecast positions are adjusted westward in repsonse to the current position of the new frontal cyclone...and are gradually caught back up to the previous outlook out of respect for the GFS. A northeast acceleration is expected later in the forecast period as the cut-off upper vortex is forecast to de-amplify back into a trough while kicked by the nearing upper trough of the central Canada frontal cyclone. I have raised peak odds of subtropical cyclone formation to 50% from 20% as Hurricane Pablo is proof that the thermodynamic profile of mild waters and cold upper air temps from upper vorticity can support tropical activity...and this system will have a similar thermodynamic profile. Also thunderstorm activity wrapped in a large band around the frontal cyclone's core is not too far from the core at the present time. Odds are dropped back to 0% by 96 hours due to cooler water temperatures along the forecast track. Regardless of acquisition of tropical characteristics or not...this storm is expected to bring large sea swells in the north-central Atlantic reaching the shores of the Azores islands...with the circulation possibly being large enough to deliver gusty winds to the islands in 1 to 3 days (24 to 72 hours) even while centered well west of the islands.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Oct 28)...40% chance of subtropical cyclone formation (central Atlantic near 41N-40W)
IOH 48 Hr Outlook (1800Z Oct 29)...50% chance of subtropical cyclone formation (central Atlantic near 41N-38W)
IOH 72 Hr Outlook (1800Z Oct 30)...40% chance of subtropical cyclone formation (central Atlantic near 42N-36W)
IOH 96 Hr Outlook (1800Z Oct 31)...0% chance of subtropical cyclone formation (northeastern Atlantic near 48N-26.5W)