MY 2019 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #172
*******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.**********
...WEDNESDAY OCTOBER 30 2019 4:12 PM EDT...
See area of interest section below for details on the strong non-tropical cyclone in the northwest Atlantic currently being monitored for acquisition of tropical characteristics.
AREA OF INTEREST #1...The impressive frontal cyclone in the northwestern Atlantic has continued to slowly weaken while under a lack of divergence beneath the central region of its parent upper vortex. To the west...there is enough upper ridging in the higher (more northern) latitudes within the eastern warm sector of a central Canada frontal cyclone such that the cold core upper vortex has become elongated and split into southwestern and northeastern halves...thus the core of the northwestern Atlantic frontal cyclone has drifted southwestward to 38N-42W in the last 24 hours while whirling into the southwestern split of the upper vortex. This has placed the frontal cyclone's core over slightly warmer 21 deg C waters...and combined with the cold temperatures of the overhead upper vortex there appears to be enough instability to drive pockets of organized thunderstorms at the frontal cyclone's core...and a subtropical storm appears to be forming. Therefore I have begun a subtropical cyclone formation forecast as outlined below. Due to the frontal cyclone center being further southwest than I previously forecasted...I have again adjusted my forecast track southward. Meanwhile...the aforementioned central Canada frontal cyclone is dissipating underneath the non-convergent center of its upper vortex...and the divergence zone of this vortex is producing a new frontal cyclone over eastern Canada. The cold air advection of the new eastern Canada cyclone will drive the Canadian upper vorticity closer to the elongated upper vortex above our possible subtropical storm...with the nearing upper vorticity kicking the elongated upper vortex and possible subtropical storm eastward during the entire forecast period. I am setting a forecast intensity of 50 mph winds based on current ASCAT passes showing plenty of 45-knot (50 mph) vectors on the northwest side of the possible subtropical storm...but it is possible the subtropical storm weakens further due to the lack of divergence at the center of the elongated upper vortex...or alternatively enough thunderstorms fire in the subtropical storm such that warm core upper outflow beneath the elongated upper vortex develops to allow the transition to fully tropical status and perhaps allow this system to strengthen like we saw with Hurricane Pablo last week. In other words since I don't know for sure if the circulation will continue to weaken or strengthen...I vote for now to maintain the current intensity. The divergence zone at the northeastern corner of the elongated overhead upper vortex by 48 hours will support another frontal cyclone either over or just west of the British Isles. For that timeframe I forecast that the possible subtropical storm will lose its closed circulation and open into a surface trough while passing over or just north of the Azores as it loses dominance to the British Isles feature due to strengthening deep-layered ridging to the west trying to capture the possible subtropical storm...making it fall behind the eastward speed of the elongated upper vorticity...thus getting weakened by the western convergence zone of the upper vorticity (the deep-layered ridging to the west in 48 hours will be due to by warm air advection ahead of the currently developing central US frontal cyclone). Albeit the latest 1200Z GFS model run has trended stronger with the circulation of the possible subtropical storm for the 48 hour timeframe...making it move east-southeastward into the Azores under the infleunce of the deep-layered ridging while still having gusty winds. I interpret this scenario would occurr if the possible subtropical storm becomes fully tropical and strengthens in the next 24 hours...thus not giving it enough time to weaken under the forecast unfavorable upper convergence before it moves into the Azores at 48 hours. Therefore in the special messages at the top of this site's home page...I have extended mention of possible impacts to the Azores into Friday.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
0 Hr Position (1800Z Oct 30)...Frontal cyclone centered in the open Atlantic at 38N-42W
IOH 24 Hr Forecast (1800Z Oct 31)...50 mph maximum sustained wind subtropical storm centered west of the Azores at 40N-35W
IOH 48 Hr Forecast (1800Z Nov 1)...Remnant surface trough located over and north of the Azores at 27W