"But seeing they could not See; hearing they could not Hear"
“The views expressed herein are those of the author and do not necessarily represent those of the National Weather Service or affiliate/related organizations. Please consult .gov sites for official information”

"From its chamber comes the whirlwind, and cold from the scattering winds." - Job 37:9.

"The wind blows to the south and turns to the north; round and round it goes, ever returning on its course".

Tuesday, September 28, 2010

POST 2: Tropical Depression 16 and Local Weather (East Florida)

(Image: NAM FCST for 2pm Wednesday)
SYNOPSIS: Frontal boundary has pushed south to roughly a Daytona Beach to Brooksville line and come to an abrupt halt. In deed, rain echoes shown on radar are not penetrating north of North Brevard County along the east coast and remain in place the past hour. During the past 3 hours atmospheric moisture throughout has increased markedly in the upper levels over Central Florida. Meanwhile, TD 16 has been proclaimed and is located 560 NM SSW of Cape Canaveral, FL.  The system is moving NNE. A tropical storm watch/warning has been issued for the counties south of Sebastian Inlet to Miami. The official forecast track takes the system offshore very close to Boynton Beach tomorrow.
Meanwhile, the mid-upper level trough continues in place to the NNW into the Florida Panhandle with a speed max  and associated vorticity plummeting south along the backside of this trough toward Southern Alabama. East Central Florida remains in a somewhat volatile environment in a battle between becoming fully tropical and maintaining a more continental weather regime in place. Per the increase in moisture, it appears the tropics are beginning to win out as the dominant player in this battle of wits, but it'll take the rest of the daylight hours and into this evening to complete the transition (if it ever actually does).
TODAY: In the interim, an outflow boundary from convection well off the Central Florida Coast has moved onshore. As such, the surface winds over East Brevard, at a minimum, have switched from light from the south to gusty from the East.... These winds are being accompanied by increased cloud coverage and radar returns and radar has really filled in, with a well defined line of convection stretching across the entire state from Port Charlotte on the SW Coast to Cape Canaveral.  Additional storms are filling in south of this line with heating of the day. Thunder booms now.
Jumping to tonight and tomorrow:
NOTES: The latest GFS and NAM forecast models are not in sync with the official forecast track of this system. They insist on this system remaining mostly as a hybrid type entity, and as such the results are much different as far as Central Florida is concerned. I've included an image for the system location at 18z (2pm) tomorrow as forecast by the North American Model. Note that the center of lowest pressure is located near the Cape. What is hard to decipher from this image is that there might be another center further south toward Indian River County.  What occurs is that the system, being that it wouldn't be fully tropical in nature, begins to interact with the trough to the north and west of Brevard and begins to become absorbed within the "mean trough' feature. As such, the current NNE track continues..with perhaps a slight turn even more toward the north during the 'absorption process'.
If indeed this system follows the track followed by these models, weather conditions north of the official forecast to Jacksonville will be significantly different from what is currently officially being announced. This is just a heads up...and not an argument. Thus, remain abreast to your most favored media outlet for details.
In either case, at this time the winds won't be too much an issue, although they could be noticeably gusty, especially in rainstorms beginning over night tonight. More so further south of Sebastian Inlet to Miami in the watched and warned areas. Close scrutiny as to what will occur once the system comes fully ashore over extreme South Florida tomorrow morning might be necessary. Again, refer to the latest statements from the NWS or the Hurricane Center for the official forecast.
And in continuity with today's earlier post. I believe there is a very remote chance of rotating storms, from near Palm Beach to Daytona (and potentially further north) along the immediate coast well prior to the more direct impacts from this system. This threat will lower as we work toward mid morning tomorrow.
AFTER THE SYSTEM PASSES: Not so fast, another bag of tricks at hand. Once this system impacts the U.S. East Coast from North Carolina to New England in rapid fashion, high pressure builds across the Mid-Atlantic Region in its wake while the Caribbean continues to simmer with rejuvenated vigor. The GFS I believe is suffering for an overdose of steroids, with multiple low pressure systems being generated down there, all of which train across the Bahamas for some time to come in the future. But tossing this aside, of more immediate interest to East Coast Floridians may be an increasing pressure gradient between this high pressure area to the north and the low down south. With those two mechanisms at work, ENE-NE winds could become steadily moderate to strong (breezy) for a prolonged period of time. The availability of moisture at this time remains in question...but the two combined could make for a windy and wet weather regime for the immediate east coast from Jacksonville to Ft. Pierce beginning Sunday near JAX and encompassing the rest of the coast by late Monday. The GFS picked up on this two days ago and has been consistent with both the winds and potential for rain showers of stratiform nature. Perhaps just flat out cloudy conditions...perhaps not. Point being, erosion could become an issue if this regime lasts for too long. Again, another heads up.
ANOTHER TOSS IN THE POT: Forgot to mention, the GFS is showing a strong tropical system to cross South or Central Florida in about two weeks, after it meanders around the Caribbean for several days moving this way and that. Accuracy for any such occurrence that far out is pretty close to negligible. Point is though, that the tropics won't be done quite yet. Not thru the first two weeks of October at least.

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POST 1: Tropical Storm Develop Much More Likely - Rotating Storm Structures for East Central Florida?

(Image: Total Rainfall forecast for 2am - 8am Wednesday shows max over Brevard County and SE Florida)
OBSERVATION ONLY: Breaking down the details very early this Tuesday and monitoring trends in RUC Model updates.
The current observation is noted. Surface front extends from Jacksonville to Tampa. Mid-upper level support for this feature has moved NNE from Alabama yesterday to West Virginia and continues north toward NW Pennsylvania. Likewise, vorticity maxima are plunging south down the backside of the trough through Wisconsin prior to sunrise with expectation this energy will penetrate as far south as Southern Alabama by early Wednesday morning. The result will be to reinforce the the mid-level trough in its current position and thus prevent further eastward progression of the surface front as its southern tip skims close to North Brevard and then becomes cut off as cyclonic circulation from the south takes the leading role. Meanwhile, Central Florida will be influenced by negative vorticity advection early on this Tuesday morning during the following transition:
1) Area of low pressure with a 60 percent chance of becoming a closed surface circulation over the Western Caribbean and its  peripheral circulation begins to drift north toward Cuba. ***UPDATE: This has just changed to 80 percent***. We could have a Nicole on our hands by the next update from the Hurricane Center. But I digress,
South Florida was never affected by the trough and front, and thus have been in continuous ESE-SE flow all along, unlike folks from Central Florida and points north. Current water vapor loops and surface observations indicate that South Central and Central Florida will be encompassed with the low level circulatory pattern between 11am-1pm today directly related to the developing system to the south. Meaning, surface winds will shift from SSW-S to a more SE-ESE component. Meanwhile,  the mid-upper level features described above reinforce the wind aloft at those levels maintaining the current SW direction overhead.
2) Transition of these two wind field parameters occurs primarily between 11am -4pm during the time of maximum surface heating, although cloud cover could be a big factor in damping out the overall convective nature of shower activity from what could otherwise be a more potent situation. During this time frame, as the outer parameter of the cyclonic circulation from the south enters Central Florida, positive vorticity advection is ushered in from the south.
The combination of low and upper level vorticity, low level directional wind shear, and influx of even greater moisture from what currently exists could harbor resultant rapidly developing small, but rotating storm cells. The affect will be maximized along the East Coast from Sebastian Inlet to Ormond Beach.
Believe the main affect of this, should it occur, would be strong, gusty winds associated with fast moving, small thunderstorms...but circulations reaching the ground can't be ruled out. This covers Tuesday afternoon, now what about over night tonight?
AFTER MIDNIGHT: The NAM and GFS continue to support the first vorticity maximum directly related to the Tropical System (by this time Nicole?) to impact Indian River, Brevard, and Volusia County between the hours of 1am - 9am Wednesday morning as further development continues. As noted, by this time we might have a named system which would add fuel to the fire. The HPC has forecast a precipitation bulls eye for mostly Brevard County during this time frame of over 1" of rain, so they must be seeing something. Believe this rainfall will come in the form of convective storms containing brief periods of heavy rain rather than a solid, steady state rain. Conditions do not look as ideal as yesterday morning for rotating storm cell structures, but should the system approaching from the south indeed wrap up as much or more than anticipated the weather radios might be blaring with Special Weather Statements or warnings while most folks are in bed.
SPECIAL NOTE: Should Invest 96L develop into a named system, the timing on the over night situation tonight might still occur, but could be a full 12 hours later, at least, than current thinking. Thus, this could take place  during the afternoon on Wednesday. Additionally, note that this is not information from official resources. Namely, I'm thinking out loud. Just providing a heads up.
P.S.: Should the system to the south develop into a named system and strengthen toward hurricane intensity, all forecasts for the state will be blown out of the water as far as wind speeds and precipitation coverage are concerned. Based on track forecasts from multiple models I've flipped thru this morning, should a system develop, the tracks are most clustered from South of Naples toward West Palm Beach, with 2 or 3 others going as far north as New Smyrna Beach on the East Coast. (opting out the other tracks taking the system toward Texas for now...but that possibility has been indicated).

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