Sub-Tropical Sean With 45 mph Winds Spits at Florida East Coast Today

Sub-Tropical SEAN is seen in this enhanced water vapor image from early this morning. The system has winds of 45mph and will likely strengthen further during the next 48 hours as it remains nearly stationary and eventually drifts toward the west to northwest before entering cooler waters. Also shown is the ridge of high pressure (zig zag line) down the East Coast into the Gulf and flow around it. Florida is in 'dry air' and our activity is not related to Sean other than very indirectly at best, but directly in the sense of the long period and large ocean swells. Cold front moving through the Southern Plains with upper level low shown over New Mexico. That low will move toward Western Michigan track the front across Florida, while the low will be far removed in NE Canada. Best chance of severe today shown in solid lavender with other areas in the dash lavender (but not all inclusive) possible. ..for presentation purposes only. The problem being presented today for severe further north is not unlike that which happens in Florida along the Magic Dividing line. The best wind profiles will be far removed in western Michigan, whereas all the instability will be near and south of the Arklatex Region several hundred miles away. The difference with these events in Florida is that the two regions are separated by, well, almost nothing.

OVERNIGHT: Decoupling and resultant drainage flow was more expansive last night with only the Cape toward West Palm Beach remaining in NE winds ( along and east of US 1), as well as a small portion of far NE Florida near JAX. Net result was cool temperatures in the low to mid 60Fs many areas as far south as Okechobee, with Homestead near Miami having the same temperature as Pensacola before sunrise. In the areas not affected by the factors of decoupling and drainage lows remained in the low 70Fs (Cape to West Palm) except far NE Florida near cooler ocean waters and less direct flow off the ocean. This can be best seen by the well past sunrise temperature schematic which shows temperatures already rising along the east coast where onshore winds of 10-20mph today will prevail...with some coastal sprinkles being the dominant mode of activity today mainly along and east of the light blue line.

TODAY: Coastal highs mainly in the mid to upper 70Fs (South Central/South) near the warmer ocean waters but prevailing mid to lower 70Fs further north. Inland temperatures in the upper 70Fs to near 80F.


Morning RUC and North American Model (NAM) forecast soundings indicate a very strong subsidence inversion just below 5000 ft this afternoon that would not support rain, with the prevalent modus operandi being banks of vertically challenged pancake stratocumulus clouds which could pass well inland and across the state. Daytime heating should lower dewpoints inland, so not sure even a sprinkle will be found west of I95 except toward South Florida. There are bigger gaps in the cloud field per satellite imagery than of yesterday, likely due to the better organization of 'now Sean' and  increasing subsidence around the western periphery (far removed from the center) as anticyclonic flow starts to encompass the storm. A sample forecast sounding shows how shallow the moisture will be today if the NAM is correct.

NOTE the dewpoint and temperature lines above and where they separate below 850mb which by standards is at 5000ft. Looks like a sprinkle day with a brief shower possible only at the beaches. This inversion was maybe 1000 ft higher yesterday at best, but every inch counts under the circumstances.  This sounding equates to spittle driplets. 

  MEANWHILE: Sean is well off to the east and is centered somewhere roughly a few hundred miles east of West Palm. Models have all seemed to initialize it too far north by 50-75 miles. No matter. The storm is nearly stationary and seems to be getting better wrapped up. Sean is meeting critieria of being a '27'...near the 27th latitude and hovering over 27C degree ocean water temperatures (which meet those necessary for tropical storm formation). Waters cool SUBSTANTIALLY north of the latitude of Jacksonville well out at sea toward Bermuda. Regardless, the storm could still become better organized and start to look more impressive on satellite imagery through Thursday.

Green line shows the western extent of the circulation per cloud types. The lavender lines along the east coast of Florida is the area that onshore winds blew all night (where the atmosphere did not decouple and/or where drainage flow was not experienced, thus warmer overnight lows). The orange arrows show the flow before sunrise. The yellow indicates low clouds or thin fog closer to the ridge axis noted by the blue zig zag.  

Per satellite animations so far this morning, it looks like the best chances for any actual showers will occur over Volusia and North Brevard toward late morning and early afternoon...but other areas could get in on the action at any time after 2pm, but not be a big deal.

TONIGHT/WEDNESDAY: Suspect that almost everywhere might fall prone to drainage flow, but a small corridor could remain free of those affects along the east coast from Canaveral to Ft. Pierce/West Palm once again. Similar temperatures with less chance of showers limited to sprinkles.


During the day Wednesday models have been agreeing that sometime between 11AM -2PM the east coast could fall within the realms of circulation of Sean as the ridge of high pressure pulls out to the NE ahead of the approaching cold front. Shower chances could exist once again mainly within 25 miles of the east coast from the North Side of the Cape to Miami. The NAM is showing ample moisture to support showers but does not depict any. Then again, that has been the case the past few days. The limiting factor though will be how shallow the moist layer will actually be. I suspect it will be a sprinkle fest at best at this point given the trends with winds more northerly with less oceanic effects. The GFS has trended downward with the rain chance.


THURSDAY: Front will be in the Panhandle and lift off to the NNE while crossing the state dragging its non-dynamic tail across the state Thursday night ... with hardly a surface reflection. During the day, winds will be NNW-NW with a cool morning due to drier air now in place due to subsidence (sinking) around Sean combined with drainage down the spine of the state. Thus, the cooler morning everywhere will be a function of lower dew points (less moisture) holding heat in as well as no wind off the warm ocean waters. High pressure in the mid-levels will build NE ward from the SW Gulf further cutting off the moisture supply, but not fully enough before generating rain along the front along and north of I-4 (at worst)...if even that.  The front will clear the remainder of the state pretty much un-noticed until after dark when winds become more NNW.


MEANWHILE: Sean will become Extra Post Tropical and move out as a gale near to or shortly after passing the Bermuda Triangle, eventually impacting indirectly the coastal NE states toward Maine and possibly even Greenland as it heads toward the Labrador Sea and Baffin Bay. Models vary from taking what is left across Greenland to merging 
SuperExtraPostMortum Sean with the other low that will be tracking the cold front across the state (noted earlier in this post), and subsequently retrograding that merger toward far northern Canada south of the Arctic Ocean!:

FRIDAY: High pressure in the mid levels continues to build in the mid-levels across the NE gulf and into the Mid-Atlantic while a surface high builds eastward from Central Texas behind the front. The two combined could send a 'wind surge' of 22-28mph down the east coast, but so far it looks like that surge will narrowly by-pass the coast by less than 15 miles. Either way, after a very cool morning low with most areas in the low 50s-upper 40s and closer to 60F only right on the beach from Port Canaveral and south, due north winds during the afternoon coupled with the already pre-established drier air will limit daytime highs along and north of the magic dividing line (Canaveral to Tampa Bay region) to the upper 60Fs and cooler north, with lower-mid 70Fs graduating (warming) the further south one goes to the Keys (upper 70Fs).


FRIDAY NIGHT/EARLY SATURDAY: Winds clip the coast all night, so the coolest temperatures east of US1 might actually be felt around 2AM and warming a few degrees as winds gradually become more onshore by sunrise Saturday, but similar overnight lows to Friday Morning elsewhere.


WEEKEND WEATHER/BEYOND: Picture perfect with winds becoming easterly post-haste by late Saturday afternoon and beyond (eventually ESE-SE by late Monday). Temperatures round the clock in the 70Fs right at the coast, warming into the 80Fs by Monday South Florida and spreading northward to much of the state Tuesday. Overnight lows warming inland as well, but will still be in the 50Fs most areas until Tuesday morning.


Next chance for showers comes Monday and Tuesday before the next front comes, in you guessed it, nearly exactly one week after the now approaching front passes per this time of year. The next front will have a problem crossing the entire state..or this is at least   possible. The GFS has shown this for several runs day after day, with the front hanging up anywhere from South Georgia to Central Florida. The easterlies to ESE-SE winds with high pressure now established due east to ESE of the state in the Atlantic and increasing moisture could make for a showery weekend before that of Thanksgiving, more 'showery' than this previous regime, but a bit warmer as well.   This is well out in time and will likely change innumerable times before then, but so far the writing has been on the wall for a more wet period heading toward the week before T-Day for a while now.