Phase 3 (?) Has Begun, Gradual Increase in Wind and Coastal Rain Chances Through Friday Evening

Image from near sunrise this Wednesday morning. A weak, but evident, low level wind surge accompanied by some sprinkles to 0.01" of measurable rain occurred shortly after sunrise along the Central Florida Coast. These initials light spritz's were followed by a rainbow to the west ..just as the final rains last Friday evening ended at sunset with a rainbow to the East. Interesting. Perhaps Florida will soon be on the wet end of the rainbow (especially the east coast) in a few days. 

TODAY: What I've referred to as "Phase 3" of an upcoming and slowly evolving pattern began this morning as a 700mb trough (at 10,000 ft) clipped the east coast from the North, related to the old upper low which has moved off the NE U.S. Coast. Associated with that trough was a NNE-NE upper level wind component (very light) and slightly cooler air at 5000 ft.  (Phases 1 and 2 were a wind shift a ground level (the surface) and at 925mb (2000 ft above ground level, or AGL). This cooler air at 5000 ft is just enough to generate a thick enough stratocumulus (stratocu) deck of clouds to put out some rain. It is pretty obvious by looking outside that above those cloud tops it remains bone dry per the blue sky which is prevalent in most locations. Colder air per the RUC (Rapid Update Cycle) model is filtering in at the 5000 ft level from Volusia County and north with all else constant, but that is the necessary ingredient to continue some sprinkles and more clouds as can be seen in the image below. As anticipated, rains ended for the Keys yesterday..but on the early end of the window of opportunity (by noon for the most part). 


Note the enhanced cloudiness further out in the Atlantic (below). Those are associated with cooler air at 5000mb moving in toward North Brevard County, which appears will arrive around the 4:30pm time frame. Thus, increased cloudiness for the North half of the state initially on the east coast will spread to the west before and during, to after sunset.  Further south, there appears to be a fairly persistent convergence/vorticity band developing off the Western Bahamas and advecting into Palm Beach County. It's hard to tell if any sprinkles are associated with that feature, but the cooler air at the 5000 ft level is not present there yet.

Some enhanced cloudiness and showers/sprinkles could occur as far south as North Central Brevard prior to or near sunset. The convergent band near West Palm might very well continue, or suddenly halt. at any time.

Otherwise, outside of the areas noted above, the remainder of  today and tonight will be similar to yesterday other than the slightly stronger wind at the surface today, decreasing a bit about 1-2 hours after sunset. Skies to remain partly cloudy this evening with more sprinkles possible from time to time. No model shows any sig (significant) changes over night.

THURSDAY: The only real difference between today and tomorrow is that the 700mb trough around 10,000 feet will have continued south to meet up with the old frontal boundary south of the Florida Straits. .possibly pushing toward the North Coast of Cuba. As it presses south, winds aloft across Central and North Florida will become more easterly at that level will as opposed to the somewhat flaky and weak NNE-NE direction of today...cooler air just above the deck and slowly increased moisture will increase rain chances to more measurable amounts from West Palm Beach to JAX from near daybreak through the remainder of the day, but most places will see plenty of sun as well outside of the showers which will be mainly restricted to 15 miles of the east coast at most. Winds to remain status quo around 15-22mph at times at the beaches and spreading inland during heating of the day, then waning and backing off after sunset. Rain fall totals perhaps 1/4" in a few select coastal locations between sunrise and set, but wouldn't be surprised to see a little more between Oak Hill and JAX.

FRIDAY: High pressure will now build more affirmatively southward from SE Canada and merge with high pressure working NE from the Deep South states in response to a very vigorous Pacific West Coast Trough pushing through the Sierras, the Wasatch, and the Rocky Mountains. As these two high pressures merge, the pressure gradient across Florida will increase as low pressure continues from the Florida Straits through the entire Caribbean and Gulf of Mexico.   With increased winds comes better moisture convergence along the east coast, especially along what appears will be a coastal trough to set up due to frictional effects of the shallower shelf waters to the 2000 ft level. This trough and increasing speed shear at the 10,000 ft (700 millibar (mb)) level results in mass moisture convergence up and down the east coast, with the strongest gradient throughout all levels directly between high pressure to the north and low pressure to the south, which currently appears will be from West Palm Beach to Jax.  

The first heavier rainshower with perhaps some thunder could occur by mid-late afternoon at the beach from Port Canaveral to JAX, although the GFS continues to have an affinity for Port Canaveral for some reason. That could easily change.

SATURDAY: Yet another surface wind surge, likely caused by falling upper level temperatures with perfectly aligned isobars (lines of constant barometric pressure) from the surface to 10,000 ft as well as the strengthening high pressure to the north will kick up the surface winds once again to a steady state of 20-25mph, mainly within a few blocks of the coast. The GFS is honing in now on the region from West Palm Beach proper to JAX for the period from Friday through Sunday to receive the heaviest rainfall in the 2-4" inch range, and restricted solely to  25-30 miles of the east coast, with slightly lower amounts in Southern Palm Beach to Southern Dade and the Keys. Actually, much lower with less than an inch in this area.

<TIME OUT: At this point, it is worth noting that during the Florida transitions, the vigorous and powerful trough moving through the West will be digging deep with plenty of very cold air with it (cold by October standards). Snow has already fallen over the Sierras and more is on the way. This cold  and very unstable air will spread east  generating snow over all of the higher elevations of the mountain ranges out west, possibly as far south as Northern Arizona in one spot, NW New Mexico, the ranges of Utah and those of Colorado included. Severe weather could occur from the Western Texas Panhandle region to as far north as South Dakota. 


Totals in the highest elevations could exceed one foot. Some folks (okay, maybe just one person) were caught off guard in the Sierras this morning, and were out putting snow chains on their vehicles in the snow.) Testament to why it pays to remain attentive to the weather, as if not heeding tornado warnings weren't bad enough.


I have mentioned the blocking pattern that will be in place over the South East states in several blog posts now. To put it in a better perspective, despite how strong this approaching trough is and will be to create all of the chaotic weather out west, even that will not be enough to dislodge that block. The trough simply lifts up and over the block into Central Canada, with another to follow during the weekend.  TIME IN>

TEMPERATURES: I have a feeling that heading into Friday afternoon both high and low temperatures could remain in the 70s at the beaches unless there are better breaks in the clouds, which is always possible.  Ocean temps in Brevard are now running at 80F, so onshore flow of at least 20mph or stronger across those waters accompanied by clouds and cool rains with gusty winds should keep the temps down at the beaches from Central  Palm Beach County and North. Additionally broken to scattered clouds should hold down inland temps to the low 80Fs, although this scenario appears more likely in the temperature fields on Saturday if things materialize as they might.  

BEYOND: Here is where we stop for today's post. If you've watched The Weather Channel or local news stations, there is much to ponder and await for regarding potential sub tropical cyclone development toward the second half of the weekend and/or the beginning of next week. BUT NOTE....

THREE SCENARIOS HAVE COME OUT BY MONDAY:

1) The GFS has now shown on various runs from yesterday to the latest as of 8AM for a low to form along the Southwestern Bahamas , to off the coast of Naples, and lastly..for one to form over South Florida.  In all cases, it seems that a wave of energy breaks off from old storm Philippe and rides along the boundary lying across North Cuba, inducing a wave of low pressure that eventually closes up into a surface low near the South West Bahamas. But when that closure is to occur is up in the air (if ever). In every case, the low is then thought to form into a depression or tropical storm, albeit a bit of a hybrid one and not fully tropical.


With that factor to consider:


1. If it moves up the Gulf Stream on the east side of the state, weather will dramatically improve for the state other than along the immediate coastal locations from Palm Beach to JAX as it passes. 


2. If it forms toward Naples and moves North the weather across the state goes dramatically down hill, with double the rainfall along the east coast (up to 9" by the time all is said and done) with the potential for low topped , mini-supercell thunderstorms capable of producing a brief tornado over Central to North Central Florida.


3. And finally, as is shown in the 8AM of the morning run of the model, the low is forecast to quickly achieve tropical storm strength, with winds as strong as 40-50 mph moving up the spine of the state   to St Augustine as soon as Monday evening, with very high rainfalls totals up to 9" along coastal Brevard, as well as the potential for mini-supercell storms created by sharply veering wind profiles in the lower levels of the atmosphere. This 'storm' would have some tropical characteristics because it does have a tiny 'warm core' (as opposed to a cold core low, <I checked out the forecast upper level temperatures), but is closed off well up to 20,000 ft if not higher which looks very suspicious.


Other runs of other models vary from no low forming at all, to two lows forming ..one near Naples and another into the Central Gulf.  The latest European hedges on the "off the SW Coast" scenario which is the one I've personally favored for the past day or so..that is..if one is to form at all. If so, rains will become more state wide with that potential for a tornado threat even if it is a good 120 miles off the west coast (especially along and east of I95).


In all cases, the unsettled weather for Florida is over by Wednesday as a low lifts north and becomes extra-tropical, dragging a frontal boundary across the state by mid-week next week. And guess where it ends up, over the Southern Caribbean. High pressure to build in back behind it and a rapid shift to more onshore easterly flow returns, this time a dry flow for quite some time.