"But seeing they could not See; hearing they could not Hear"
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"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".

Thursday, January 20, 2011

The Florida Current and Loop Current Affecting Florida Weather

Images: In first image, The Florida Current is shown in black, with the Loop Current sketched in red. Second image is the forecast for late this afternoon. I've drawn in weak low pressure areas in purple (not provided by auto-output), note the correlation of these lows with the warm, ocean currents shown in the first image where red "L"s have been drawn. I've also drawn in a black dashed line off the Florida east coast in the first image. This is the nuisance "inverted trough" often referred to in posts that forms above the warm waters of the current.

RECAP: Weak frontal boundary crossed Central Florida during the late afternoon. The immediate East Coast from near Cocoa Beach to Jacksonville was "backdoor'd" with a very cool wind immediately behind the boundary from the northeast (rather than the normal northwest post-frontal wind) which advected a very cool near shore marine layer to the coast lowering temperatures there into the 60s while others remained warm until well after dark to the west and especially the south where they've barely even been phased by the front, if at all. The layer of cool air over Central Florida is extremely shallow though (almost laughable), with the KSC sounding showing this morning (and last night) that it only extends vertically about 800 ft with warmer air and a WSW-SW wind still in place above this shallow inversion that had been at the surface preceding the front.

TODAY: Some fog (dense in a few patches) and low clouds should burn off pretty quick this morning with temperatures recovering everywhere to yesterday's levels, except along the immediate east coast north of Patrick AFB where a light onshore seabreeze will keep it a bit cooler along the A1A corridor. Otherwise, little 'action' to speak of in the short term. Do expect continued partly cloud skies though with ample low level moisture still in place and lots of sunshine minus high level clouds. Could even see a light rain shower move in along the west coast and/or form near the east coast (especially south) during the course of the afternoon and through the night, but of light intensity and short duration).

Meanwhile, a cold front will be located as shown in the image above. Do expect a very weak surface low (and likely more than one) as shown with the purple "L" on the map, as well as an associated pre-frontal trough (the dashed black line) to form today. Also note the other purple "L" off the Carolinas. Both lows are forecast to form over the warmer ocean waters of the Florida and Loop Currents, very common. The low off the Carolinas, of which many have either generated or developed there, will ride up the eastern seaboard again creating wintry conditions for the East Coast of New England as it converges with another system way out of the picture for Florida's concerns and beyond the scope of this blog today.

TONIGHT: Light sea breeze near the coast becomes south to SW after sunset once heating of the day has relaxed and thus the dynamics for sea breeze formation are lost. Cold front and preceding prefrontal trough/low(s) approach the west coast of Florida near midnight and quickly spread associated moisture in advance across mainly North and Central Florida such that an area of rain, and perhaps embedded, elevated thunder forms between the hours of 12am - 4am. By sunrise fully expect to see all of the North Half of Florida under some form of a rain/thunder/clouds mix along and north of a line from Tampa Bay to the Space Center, give or take 30 miles either side (north/south). Overnight lows mild due to increasing cloud cover after midnight in WSW flow aloft.

FRIDAY: Possibly more than one weak low pressure system, more likely 'impulses' (which we'll never see on TV) will run across Central Florida along first a weak pre-frontal warm front, then again along a pre-cold frontal trough. Best chance for thunder at time for the immediate Central Florida area seems to be from 4AM - 9AM, with mainly rain after that. Models indicate the actual cold front will perfectly bisect the state no later than mid-morning, and get hung up there for the remainder of the day as it becomes entrenched in parallel flow from the WSW aloft and blocked by high pressure over the SW Bahamas and Cuba. Likely additional impulses will ride along the boundary, generated above the Loop current and weakening after crossing cooler water before reaching the land mass of the Florida Peninsula. But they can transport moisture to continue cloud coverage and showers/rain through the day, even just behind the front. These lows may also restrengthen to a small degree after moving just off shore and entering the Florida current/Gulf Stream waters, placing the east coast in backwash circulation even within the cooler sector (behind the front).

Believe that South Florida or roughly from West Palm Beach to Sarasota and points south toward Lake Okeechobee will have a shot at thunder any time after 1pm through the remainder of the afternoon hours, especially further south where cloud coverage should not be as extensive early and better surface heating, and thus air mass destabilization can occur. The main threat from any thunder activity at this time appears would be marginal severe winds, but given that mid-level winds are not forecast to be above 30-40kts severe category gusts should be isolated. Lapse rates/ decrease in temperature with height / overall destabilization do not look very impressive, but Convective Available Potential Energy could reach 1000 J/kg (Joules per kilogram) which is equal to the amount of CAPE down there on Monday while they were in a Tornado Watch. Difference this go around is the wind profiles do not look, at this time, to be as favorable for potential rotation in any strong updrafts. But bears watching. Despite all the possible rains and maybe some thunder north half of the state, my eyes are more pegged toward South Florida Friday afternoon given the above.

Need to point out that the amount of time the front remains fixed across Central Florida is not in close agreement between the models I'm seeing early this morning, but it does looks like the front will gradually press offshore for all but extreme South Florida after sunset, but continuing to hang up parallel to the Gulf Stream offshore. With this in mind, and considering yet a nearly 'representative' surface low could form off the East Central Coast, we might be looking at continued cloud coverage along the east coast, and maybe even some rain showers until mid-late morning time Saturday until the next upper level kicker well to the north scoots the assembly en masse out of here.

SATURDAY NIGHT-SUNDAY: Brief period of possibly windy conditions overnight once the kicker, accompanied by stronger mid-level winds crosses over night, Saturday. Quick shot of cool air over night Saturday into early Sunday with a quick recovery leading into Sunday night and Monday as winds swing around to the SE once again preceding the next system that will have already been coming together in the West Gulf while the coolest air is over Florida.

MONDAY-TUESDAY: Not waiting for latest guidance, as during the past 24 hours the GFS has varied in timing/intensity of the next system. Most significantly in timing. The latest run brings the next system in Monday afternoon-evening which looks awfully fishy (and faster than previous runs). As such, decided just to deal with the short term and let the next few model runs come closer together with what will be coming early next week, which of course will be addressed in every future post. May very well find that when the morning model run comes out that it will have doubled back on itself, or in other words, re-assumed its previosu train of numerical, cyber-reasoning.

Interestingly though, the next system isn't looking as 'threatening' as thought might come together, but then again, it's the one after that (Thursday/Friday) that looks even more so than what Tuesday's appeared it ever would be. In other words, the conveyor belt of rain producing systems continues through next week with storm systems every 3-4 days, but no real cold air of great significance/long duration. This will continue until the mean, positively tilted trough well aloft that dictates overall storm system motion moves east of it's current position which is diagonally across the country's midsection from the Great Lakes to the Desert Southwest.
Not to say we won't have a pretty cold morning or two, but nothing indicates prolonged entrenchment of cold air until at least NEXT weekend (not the one coming up).

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