*******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 7 2019 3:12 PM EDT...
See area of interest sections below for areas being monitored for 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 is transitioning into a surface trough supported by a broad area of upper divergence between the north side of the upper ridge cell and east side of the upper trough approaching from eastern North America. This disturbance has been introduced into the National Hurricane Center tropical weather outlook while putting this birdseye view post together...therefore is not marked in the above birdseye view chart. So far I still do not expect tropical cyclone formation from this disturbance due to wind shear from the approaching upper trough and as it loses its definition from the low pressure field of area of interest #2...but heavy rain with isolated flash flooding cannot be ruled out for western Cuba...the Florida peninsula...and western Bahamas in the next day or so. And finally the NAVGEM and Euro models have been suggesting that tropical cyclone formation could occur in the eastern tropical Atlantic during the next week...and recently the CMC and GFS models have joined in. Conditions for development will be generally favorable here in the next days due to an upper ridge cell persisting in the region...therefore if the current tropical wave emerging from western Africa continues to produce widespread and somewhat organized thunderstorms then I will be introducing it as an area of interest for tropical development in my next update.
AREA OF INTEREST #1...Surface cold front and upper trough in the central Atlantic beginning to evolve into a cut-off deep-layered low pressure that will likely acquire tropical characterstics...continuing to monitor this area for subtropical cyclone formation in the coming days. The cut-off is occuring due to deep-layered western Atlantic upper ridging to the west...induced by warm induced by warm surface southerly flow ahead of a strong eastern Canada frontal low. The deep-layered ridging is expected to drive the cut-off deep-layered low pressure west-southwestward in the next 48 hours. Although the surface circulation of the deep-layered low will reach the surface ridge weakness of the system in area of interest #2 by 72 hours...I hang on to a southward angle in the forecast track by that time as the surface circulation reaches the west side of the upper part of the circulation where some northerly upper winds could affect the steering. I then turn this system northwest by 96 hours into the ridge weakness after the surface circulation completely decouples and escapes the upper-level circulation. My forecast track is nudged westward due to the current position of the developing surface frontal low which will soon become the surface circulation of the deep-layered low. Although the cut-off deep-layered low is expected to initially form over waters typically too cool for tropical development...the cold temperatures of the upper circulation (upper vortex)are likely to de-stabilize the atmosphere for thunderstorm activity and tropical characteristics to develop. I begin to show weakening at 72 hours while the surface circulation moves into the less favorable convergent west side of the upper circulation. At 96+ hours this system is likely to lose its identity to the low pressure field of area of interest #2...but will be moving into favorable upper winds directly below an upper ridge cell induced by warm air advection ahead of area of interest #2. Therefore I do wonder if there is potential for this system to make the transition from subtropical to fully tropical before fully losing its identity.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
0 Hr Position (1800Z Oct 7)...Frontal low centered at 32.5N-45W
IOH 24 Hr Forecast (1800Z Oct 8)...Frontal low acquiring tropical characteristics...centered at 31N-46W
IOH 48 Hr Forecast (1800Z Oct 9)...50 mph maximum sustained wind subtropical storm centered at 30N-52W
IOH 72 Hr Forecast (1800Z Oct 10)...35 mph maximum sustained wind subtropical depression centered at 29.5N-56W
IOH 96 Hr Forecast (1800Z Oct 11)...Remnant low centered at 31N-59W
AREA OF INTEREST #2...An area of rotating showers and thunderstorms currently north of the Bahamas and offshore of the southeastern US remains supported by divergence on the east side of a cut-off upper trough in the area...but as this disturbance interacts with the large amplifying upper trough approaching from eastern North America it is expected to evolve into a powerful non-tropical cyclone offshore of the eastern US. Therefore regardless of whether or not this system later transtions from non-tropical to subtropical...I recommend preparations on the eastern US coast...particularly on the New England coast...for coastal sea swells should be starting as this system will be generating notable ocean effects beginning in 48 hours. I have begun a subtropical cyclone formation forecast as I believe conditions are going to be favorable for this system to acquire some tropical characteristics in the coming days. In the next 24 hours...this disturbance appears it will continue slowly drifting north-northwestward under the influence of the strong surface ridge in the western Atlantic...and as the cut-off upper trough gravitates northwestward toward and eventually merges with the much larger upper trough currently approaching from eastern North America. In 24 hours this disturbance is expected to transition into a frontal low along the cold front associated with the large upper trough. What happens after that time is expected to be significant as it appears imminent that a round of amplifying warm deep-layered ridging to the west and north should amplify the the upper trough...with increasing divergence on the east side of the amplifying upper trough rapidly intensifying the the frontal low. This warm deep-layered ridging is expected to be induced by plenty of warm air advection ahead of a strong forecast frontal cyclone to form over central Canada (currently the energy for this forecast frontal cyclone lies with an amplified upper trough over western Canada). The modeling has shifted further east in the long run (further offshore from the eastern US coast)...and by studying today's and yesterday's 1200Z GFS model run it appears this is due to the stronger surface trough associated with the disturbance emerging into the southeastern Gulf of Mexico from the northwestern Caribbean Sea. The GFS initially shows the frontal low that is expected to form from this disturbance becoming more entagled with the low pressure field of the disturbance heading into the eastern Gulf...thus keeping the frontal low further south and west. The further south location means the frontal low's west side will not be able to pull as much cold air southward...thus the cold core upper trough is now forecast to never fully amplify into a cut-off upper vortex...and upper troughs when compared to a fully closed upper vortex tend to move eastward while more readily hooking up with the mid-latitude westerlies...which correlates with the longer term eastward shift in the models. Thus my updated forecast points are adjusted southwest in the short term and eastward in the longer term to account for the recent model trends. The cold temperatuers of the upper trough are likely to cause thunderstorm activity despite the mild water temperatures...therefore I forecast transition to a subtropical storm by 96 hours. I show no loss in strength between 96 and 120 hours as this system moves eastward with the supportive eastern divergence zone of the upper trough. This system will likely have a large and strong wind field...in particular on its north side...due to the tight pressure gradient against the deep-layered ridging to form to the north and west. The tremendous wind field on the north side will be blowing towards the northeastern US shore which is why ocean effects (sea swells..storm surge...waves) along the coast are such a concern.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
0 Hr Position (1800Z Oct 7)...Rotating thunderstorms in the vicinity of 29N-69.5W
IOH 24 Hr Forecast (1800Z Oct 8)...New frontal low centered east of North Carolina at 35N-70W
IOH 48 Hr Forecast (1800Z Oct 9)...Frontal cyclone centered offshore of the eastern US coast near 36N-69W)
IOH 72 Hr Forecast (1800Z Oct 10)...Frontal cyclone centered offshore of the eastern US coast near 36N-70W)
IOH 96 Hr Forecast (1800Z Oct 11)...60 mph maximum sustained wind subtropical storm centered offshore of the eastern US coast near 36N-68W)
IOH 120 Hr Forecast (1800Z Oct 12)...60 mph maximum sustained wind subtropical storm centered at 37.5N-65W