"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".

Saturday, October 8, 2011

Storm Focus Shifts to South Half of Florida - No Tropical Development Expected

"LARGE TREE DOWN" - Cape Canaveral from Friday Evening Winds estimated to gust to near or over 60mph, and likely stronger (considering the above)

TODAY: Evolution is under way with sunrise of  overall future features as models come to agreement.

No real surprises. It does not appear that a truly tropical or even sub-tropical system will form, but if one were to be named it would likely be 'fictional' as was Hurricane Irene for which land based surface observations never verified sustained hurricane force winds, only in gusts. Any low to form will have strong winds not due to a tight circulation and low central surface pressure but rather from a tight pressure gradient in the mid-levels translated to the surface in wind gusts near and in stronger rain showers and thunderstorms...far removed from the center of lowest pressure.

OVERNIGHT: Heavy rainstorms with lightning occurred almost all night, mainly across Central and Northeast Florida. Rainfall totals so far have been between 2 -7", with somewhere around 1.5" being the overall overage across the East Half of the state north of West Palm Beach. By the time I'm done writing, they could go up another 1" in some places though. 

There were some chosen locations in Flagler, Volusia, Brevard, and south to Martin County that have run above 4" though. Winds in the stronger storms were reported generally in the 40-50mph range, but the storm we had here last night definitely had wind stronger than attested to the image above of a tree that stood up to the 2004 hurricanes.

Quickly, the graphic below was saved to show how varied conditions are close to the coast overnight compared to well inland. A coastal/marine trough forms near the coast which is along where the heaviest rain fell.

NOTE winds of 6mph inland and a steady 20mph at the coast outside of rain showers. I labeled the purple line as " the nocturnal coastal trough". Formed by wind convergence along the beaches along sinking/subsiding air inland overnight where it cools...and between where the air remains unstable closer to the coast and the warmer ocean waters (aided by the Gulf Stream)

And Aloft, as the Easterly winds blow along the ground,   is the jet stream and divergence creating lift for the air mass below a flower opening its petals.

It is within this upper level trough area the main 'feature low' will form, perhaps closer to the west coast, but two or three smaller surface lows could form between today and late Sunday along the surface boundary further south.

TODAY: At time, all factors are now in place for a more organized low pressure to evolve, and more factors are on the way through Sunday. It appears this will occur along the old frontal boundary of last weekend which ended up in the southern Florida Straits. High pressure is centered over the Mid-Atlantic with the cold front out west not expected to enter Florida until Thursday through Friday. Up until that time, showers and thunderstorms could occur. 

However, the days of strong onshore easterlies along the coast will end from South Florida To North from late early Sunday working north toward Monday afternoon with time, as will the onshore moving rain-shower regime.

Old front could return as a pseudo warm front. Strongest storm activity, and thus the focus of weather activity, will be along and north of this boundary with time going through today into Monday. Low pressures seems to be located both WSW of Naples as well as in the Southern Bahamas...both sides of Southern Florida
As noted, the focus should shift from onshore moving rain storms solely to those along and just ahead of the boundary to move north from the Straits. Already, there is a tornado warning out toward Southern Dade county based on radar. 

The image above is from the RUC model and closely matches that of other models. Note the strong winds to the north of the boundary (the blues and purples with stronger winds indicated by the wind barbs within those colors) . 

That stronger wind appears to be headed toward South Central Florida today through Overnight Sunday. Otherwise, the main feature outside of this boundary will be low pressure aloft in the East Central Gulf. It would be far too extensive to describe how the models vary, because they all do. But there does seem to be some sort of agreement that there will be weak surface lows along BOTH coasts embedded within a large mid level circulation, which as it would be, will be located near the base of an even larger trough created by a merger of the southern and north branch jet streams. As that low /trough lifts north so will to the surface boundary 6-7 miles below it. More storms could occur along SE Florida, with some heavier rain showers as far north as the Cape.

As the main upper low wraps up and gets organized, it will draw warmer air into its upper circulation, thus the air mass will become less thermodynamically unstable; however, as these lows organize,  wind shear/bulk shear through levels of the atmosphere, and in turn helicity will increase especially on Sunday through overnight Monday as the warm front (or so I've called it here) lifts north and meets the stronger baroclinic zone across South Central Florida. Again, according to the NAM model, not a given.

The Storm Prediction Center has Southeast Florida in a Slight Risk for Tornadoes Today and into  tonight for these features, but a smaller risk area extends toward the Cape area. Any tornado will be isolated if  at all, but the wind risk will become, from how I see it, quite real in any storms that can form especially tomorrow into early Monday morning post-midnight across South Central Florida, especially near the coast and inland as far as I-95. There is quite a show going on right now near Homestead with a big storm.

Elsewhere, another wind surge looks to be in the cards as I write to approach South Central Florida by 2-3 pm. Winds will be strongest where they have been all along, namely within 1 block of the beach and along the west banks of the Banana and Indian Rivers in exposed areas. Winds in heavier rainstorms could gust to 40-50mph, although with the upper levels warming more, I'm not seeing as much lightning any more except with the storm that was tornado warned over South Florida and a small bit off shore. There was much more lightning last night and early this morning before the upper low started to ingest warmer/tropical air. Already, winds at the beaches such as Patrick are gusting to 39mph last hour without the help of a rain storm...while away from the beaches winds dropped off gradually further from the coast. Winds are also stronger near the West Coast. 

SUNDAY Weather should improve over South Florida, but could go down hill from near Ft. Pierce after sunrise and north to Port Canaveral later in the afternoon as the boundary is lifted north and up the peninsula. As a heads up:

BASED ON THE NAM ONLY, which tends to go over board and has not been too reliable lately, this is the worst possible case scenario on Sunday:

A slight risk for tornadoes could be at hand by mid-morning north of West Palm Beach, with that risk extending as far north as Port Canaveral by Midnight if not sooner. If South Florida is in a risk area now, that is 'nothing' compared to what the NAM shows to evolve between now and tomorrow. 

The only thing NOT going for a more assured RISK is that instability will be greatly limited, but not completely. However, low and mid-level helicity,  increased moisture in the low-mid levels, BULK shear from the surface to 700mb, and even some angular momentum indicated by the 850-700mb wind barbs and timing of night along the nocturnal, coastal marine trough which develops at night would all add up to some pretty darned vicious storms. Again, this is based only on this model. With the 'tools' I have availbe, it is the only one that shows all of the parameters needed to be known to make such a determination. It may very well be though this period will be just like all the past two days, but I'm having my doubts about that. The NWS in Melbourne is making no mention of it, much to our relief. At least, not yet.

The worst weather appears could occur from Ft. Pierce and working north to Port Canaveral between 11AM through 4AM Monday morning, and extending as far west as a few miles west of I-95 toward the county lines. After that point , the threat diminishes as portrayed by the NAM as the low level boundary gets further removed from the upper level low over the Gulf of Mexico. But, there is still much to be learned, and plenty of time to learn of 'it'.

BEYOND: Outside of this ongoing saga, it appears a shift in the overall hum-drum will occur overnight Sunday through Monday winds die and shift to a southerly component of only a light wind compared to these past few days. In other words, normal wind and even normal to warm daytime highs on Monday outside of the JAX area.  The cold front will be on the approach, but the entire peninsula could be good for afternoon and evening thunderstorms, favoring the east side from mid-afternoon through late night each day through Wednesday.

The GFS has a prefrontal trough to go through Central on Thursday, with the actual front on Friday. The weather on both of these days across Central will depend on the time of day each one is to pass. So far, two consecutive runs of the GFS show the prefrontal trough which could be weather active to cross Central near sunset Thursday with the actual cold front to cross before noon Friday. South Florida will likely get the benefit of getting better rains from both features, but not exclusively.

NEXT WEEKEND: Looks to be everything this weekend is not, and what last weekend was.

Thunderstorms and squally rains rotate into the coast before sunrise this morning. They seemed to take a slight cyclonic like curve as the approached the coast (and the nocturnal coastal trough) which was pushed west toward the banks of US1. Heavier rains fell on the lee of that trough in Rockledge toward Sebastian Inlet.

"Utter and Total Devastation " (as far as the fence is concerned) . It just recently collapsed to the ground while typing the post today.

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