TONIGHT/THURSDAY: There are two general camps model guidance is hedging on regarding what happens in the Gulf, for what happens there will determine what is to happen over Florida and where it does what.
One camp has the low moving more toward the north. The latest HRRR model which is High Resolution and short term shows that to be the case as does the NAM model. If this does occur, the chances of severe like weather in any form, including flood potential in vulnerable areas goes to nearly zero.
The latest HRRR seems in fact to be developing something akin to a Tropical Storm with a well formed eye in the next 18 hours. With that said, this post will focus on the other scenario indicated by the Canadian Model (in regard to direction), the ECMWF Operational and Ensemble Suite combined with the latest morning GFS which is just being made available on the internet as this is being typed. So far, the latest GFS in the ' general details' agrees with the Euro to not develop the system much more but rather keeping the system rather 'open' in the mid-upper levels which seems more rational given how right-handed the storm is. The center is in fact shown to be in rather dry air at this time. Thus, the track (if this continues to be the case) of the surface low is not nearly as important as noted previously as the weather that will or could occur to the 'east through nearly south of the low center' as it tracks according to those models toward the Big Bend region north of Cedar Key.
TONIGHT: Per the GFS, some 'inclement weather' could begin to impact the SW Florida coast as soon as post sunset today. Latest radar is showing some rather strong storm cells well SW of this region as I write only making slow progress. The biggest issue occurs well after midnight and then more so after 10AM Thursday morning as the mid-level low 'expands' and sends a mid-level like 'warm front' northward coincidental with a low-level jet like feature. The end result of that boundary is to :
1. keep S-SE surface winds intermingled with increasing midlevel SSW-W winds of up to 6o kts not far overhead, turning with height; as well as to .....
2. draw unstable air northward toward Central Florida. Guidance continues to indicate the heaviest rainfall along and near of I4 but there is very little convective instability in that area. Thus, a low Cape/High Shear environment exists there per this model run for low topped supercells as well.
The secondary additive 'factor' to be watching is along and near the Central Dividing Line running in this case from Near Tampa Bay to Cape Canaveral/Port St. John where the GFS (Global Forecast System) shows decent instability creeping northward after sunrise making it to about that line. That is, if in fact the instability performs as shown.
This would :
1.set up a local mesoscale dynamic boundary overlaid by increasing directional wind shear as well as speed shear from 2000-15,000 overtop that unstable air mass at the lower levels;
2. Thus, resulting in Bulk Shear values exceeding at times 50kts in a narrow corridor across a part of Central and high very high helicity values, both of which are conducive for rotating thunderstorms.
That is, if the latest GFS stands correct.... Noting that these values are in INCREASE since the previous post, thus upping the ante on the potential tornado threat from mini-supercells if not full blown ones at the rate that model is going which looks a bit far fetched, but embedded as well in cloud coverage.
This is a worst case scenario though, at least so far. It is worth nothing that storm activity will likely be embedded in perhaps light rain and extensive cloud coverage, and thus will not be easily discernible to see from a distance with the naked eye. Man your TV radar stations.
Again, all hinges on what the low in the Gulf eventually does. Interestingly, another player in the puzzles is high pressure aloft to form east of Florida which increases the 500mb pressure gradient. That is a new player likely responsible for the increase in bulk shear through all the midlevels of the atmosphere since the previous model runs, and is suspect.
This post will not go into other values such as horizontally spiralling helicity values, but will leave a mention that the National Weather Offices are fairly 'impressed".
TAMPA'S OFFICE: "OVERNIGHT...BOTH THE GFS AND ECMWF CONTINUE BUILDING WIND SHEAR AS THE LOW LEVEL JET BEGINS TO BLANKET THE AREA WITH 0-1 KM HELICITY OF 100 TO NEARLY 500 M2/S2 FROM SOUTH TO NORTH BY 12Z THURSDAY. THE 06Z GFS FEATURES 0-1 KM BULK SHEAR VALUES OF 35-40 KTS AROUND THE TAMPA BAY AREA AT 12Z THURSDAY. THE EVOLUTION OF THE POTENTIAL EVENT WOULD CONTINUE NORTHWARD AND EASTWARD AS THE CENTER STARTS HEADING TOWARDS THE COAST OF THE BIG BEND OF FLORIDA. THIS EVENT WILL NEED TO CONTINUE BEING MONITORED AND SMALL CHANGES TO THE LOW TRACK AND HOW MUCH AVAILABLE INSTABILITY WILL BE AVAILABLE FOR CONVECTION.
MELBOURNE'S OFFICE: TONIGHT..".06Z GFS INDICATED THAT BANDS OF HEAVY RAIN MAY BEGIN TO AFFECT PORTIONS OF THE AREA LATE TONIGHT AS LOW LEVEL SOUTH TO SOUTHEAST WINDS INCREASE. MODEL GUIDANCE SUGGESTS THAT THE NORTH HALF WOULD BE MUST UNDER THE GUN FOR HEAVY RAIN...BUT AM CONCERNED THAT A CONVERGENCE BAND COULD ALSO SET UP NEAR THE SOUTH COAST. THEREFORE WILL ISSUE A FLOOD WATCH BEGINNING LATE TONIGHT FOR ALL COUNTIES.
A PSEUDO-WARM FRONT WILL LIFT NORTHWARD INTO CENTRAL FL
INCREASING THE LOW LEVEL SHEAR WHICH SHOULD ALSO PRESENT A THREAT
FOR ISOLATED TORNADOES. PEOPLE IN EAST CENTRAL FLORIDA SHOULD MONITOR THIS DEVELOPING WEATHER SITUATION TONIGHT THROUGH THURSDAY.
INDEED...MODEL GUIDANCE INDICATES VERY HIGH HELICITY VALUES BTWN 12Z THU AND 00Z FRI (300-600 M^2/S^2) ALONG WITH RESPECTABLE CAPE VALUES (BTWN 600-900 J/KG N OF I-4...BETWN 1600-1900 J/KG ALONG THE TREASURE COAST). A SOLID 45-50KT S/SE FLOW THRU THE H85-H70 LYR BCMG S/SW BTWN 18Z THU AND 00Z FRI IS A NOTEWORTHY INDICATOR AS WELL. FL RESIDENTS AND VISITORS ARE URGED TO REMAIN UPDATED WITH THIS DEVELOPG WX SITUATION. "
Do note the above discussion was written for the 06z model. Since that time,
it appears the values noted have increased on the GFS run just now coming
BEYOND: As the low 'supposedly lifts up the east sea board it will leave a
boundary behind with plentiful moisture making for a continued chance of
afternoon thunderstorms, esp. near the East coast and warmer temperatures
as high clouds and their coverage will be out of the picture through the
weekend. By Monday the ridge axis lifts north to where I appears most activity will be over the interior, at least for a day or so.