"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".

Sunday, October 9, 2011

Watching Weather Conditions For This Afternoon Central/North Central Florida

There is a large 'blob' of convection off the East Coast of South Central Florida at noon. It appears to be located/resultant from upper level divergence and low level convergence at the negative tilted base of the 200mb (40,000 ft) jet stream flow. Other convection along the SW Coast of Florida seems to be associated with a 500mb low within this trough.
There lies the 'potential' for the branch flow in yellow to weaken and/or cut off, at which point convection along the Florida east coast could stream inland. Mainly after 2pm. The latest 18 hour RUC simulated radar animation is showing showers with embedded thunder to stream in mainly near the north end of the CAPE, well inland to the west coast from that point as the flow around the low off the SW coast takes over the steering currents.
The latest HRRR model (which runs several hours slow unfortunately) is bringing 'some' activity on shore, to lesser extent, but stronger from Indian River County and north, with ONE strong storm moving across Central to North Central Brevard late in the afternoon.
Thus, although little to no rain is occurring at this time..or is mostly moving out, this could be because the low off the SW coast is wrapping up (closing).
Heating is occurring in cloud breaks for the time being, but some high clouds are working toward the East coast near Brevard.
Latest water vapor animated loops show much of the state is being 'dry slotted', however, SPC Mesoscale analysis shows that there is ample moisture in the convective layers between the Lifted condensation level and the level of free convection.  A pseudo warm front is moving slowly up the state from far south Florida at noon, and winds at the surface are responding to the tightening pressure well as backing a bit more toward the NE in Northern Brevard (for example). Winds aloft below that level are more from the East to ESE.
Any severe weather to occur will likely happen in a very restricted area (if it does at all) right ahead to right behind the surface boundary.
This is just a 'precautionary' post. The situation would be much more clear if we were dealing with a strictly tropical or strictly non-tropical situation, but this one is neither. Models did not handle the precipitation fields well in regard to where the heaviest rains would occur for this event, but did handle the latitude at which they would. Osceola County likely owns the highest rainfall totals. For this reason, even today's events if they occur at all are highly questionable.
Another area to watch is interior SW Florida.

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Windy With A Small Chance of Severe Category Storms By Noon

Current conditions as of 5AM. The trough still appears to be more of a 'warm front'. The image annotations are described below in the over view / explanation portion.  Note how TIGHT the isobars are compared to previous days.

TODAY: Very windy, mainly at the beaches through noon, but spreading well inland by noon. Winds should increase with sunrise and spread west toward the interior, especially north of Lake Okeechobee to the Beachline by mid afternoon. Generally, winds within one block of the beach and along the west banks of the Banana and Indian Rivers in exposed areas will be in the 24mph range with gusts toward 40 -42mph. ALTHOUGH, I saw an observation last night out of Virginia Key east of Miami reporting gusts to 52mph. Something to be advised of. This was likely related to heavy rainstorm activity in the area.

As I type, I can actually see stars?! While showers are inland and some strong rainstorms  are further south not far away.

Very little change in the line of thinking from yesterday's post. This post includes agreement with comments relayed by the National Weather Service Offices in MIA and MLB, which surprisingly were what was written here yesterday. They also are in line with those from the Storm Prediction Center (SPC) based in Norman, Oklahoma, which also match yesterday. Those being:

1) The SPC refers to the boundary near South Florida as a 'warm front'. This boundary will lift north from its eastern flank while moving little on the western flank which is embedded more toward a supporting upper level trough. Thus, this boundary will 'pivot' from the western flank while the eastern side will lift north and west during the day. As it does so, the pressure gradient between high pressure to the north and low pressure associated with the boundary will increase, thus the high wind threat. This will occur during the late morning through sunset.  In doing so, helicity along the northern lead of the boundary will increase, but mainly in the levels of the atmosphere above 2000 ft to 12,000 ft, whereas at ground level winds will be quite unidirectional (from the same direction). However, with any minor ripple or glitch in the current line of thinking there could be a threat of an isolated tornado. 

The purple area in the image above is where it appears that threat will exist between 2pm - 7:30pm, although it could be earlier than this for the region along the south end of the outlined area. 

The second reason to downplay a tornado threat as noted yesterday is that thermodynamics (instability/buoyancy) will be lacking due to lack of heating with cloud cover that is expected. The biggest threat areas though should be within 20 miles of the coast (east coast) where any long lasting and better breaks in clouds might occur. More appropriately, up to 10 miles DOWNSTREAM of where those breaks occur.  Any storm that might contain thunder should be a red flag today, but that too is questionable (thunder).

This is SPCs thinking  , as noted :  EXPECT NUMEROUS SHOWERS WITH 
SRH (Storm Relative Helicity) INCREASES.

This is their threat area in the image below. I threw in my own 'slant' for a 'threat area' 
of possible tornadoes as well in blue, but realize the SPC outlook is official.

Outside of the conditional tornado threat, any storm today with thunder could be severe thunderstorm warned if conditions warrant for 'winds' in excess of 58mph, since this
activity would not be related to fully tropical activity. This very well may be the case, 
but again, the question becomes, "can we even get thunderstorms in here today with 
warmer air aloft/less instability? The GFS implies there will be some instability, whereas the RUC which has been doing plain awful since yesterday, says 'no'.

THE OFFICIAL SPC OUTLOOK From Early Morning is in Green. This might be removed by 8AM though, but I doubt it. One can never be too careful in these instances.

2) The NWS Melbourne is also mentioning this threat in their early morning discussion, 
possibly because SPC had. They have mentioned it in the past though, but for a different reason.This treat looked real enough yesterday for the reasons cited this morning though for it to be mentioned in yesterday's post.

SOUTH FLORIDA: Winds here from Palm Beach and South will decrease significantly 
with the passage of the warm front 'like' boundary. It appears this should occur by noon 
time. In fact, it will not be windy at all once it clears. Rain chances also diminish greatly, but some stray showers or even a thunderstorm 'might' occur. Temperatures aloft have 
warmed as noted yesterday , hence the lack of thunderstorms this morning and the other reason why the tornado threat is conditional.

CENTRAL FLORIDA: Front pivots from the western flank, with the eastern flank lifting 
north and west. Pressure gradient increases further across South Central/Central Florida. Rain showers and possibly thunder could form/increase after sunrise, although some areas might not see rain at all until at least noon if ever.

Pressure gradient. At this time, the barometric pressure near Tallahassee is 30.10". In Ft Lauderdale it is 29.80". The gradient is the degree of difference between those to 
numbers. On a normal summer day, they run close to identical. 

The warm front is expected to lift north of the Beachline around sunset or shortly
thereafter, at which point winds quickly wane , followed by waning rain chances as well

Further north, rain chances toward the east coast from Volusia County and north could 
continue past midnight but end by sunrise.

MONDAY: During the day , the boundary will have swept into the Gulf and become 
aligned NE to SW in the Gulf close to the upper level low. A weak but broad surface low will form from the mid-levels down to the surface of non-tropical nature, although this is debatable. Another low could exist near the Florida Panhandle along I-10 east of 
Tallahassee. Monday will be quite pleasant with standard fare land breezes in the morning with a South to SSE wind nearly paralleling the coast in the afternoon. Some 
thunderstorms could form under the conditions, but rainfall should not add up since storms will move from the SW at 15-20mph. Most likely, late in the afternoon , and could last 
until after dark, around 9pm.

TUESDAY/WEDNESDAY: Similar to Monday in the wind department as the low in the Gulf lifts NNE toward the Big Bend. This low will have a surface trough with it, a bit like a 
'pseudo cold front'. My line of thinking now is that thunder will be more likely Tuesday 
with this boundary and moisture still at play. On one or both days some of these storms 
could be strong along and east of I-95. The low will lift north through Georgia and along 
or just east of the Appalachians, with a secondary low running up the eastern sea board 
eventually toward the Statue of Liberty/New York early in the week.

THURSDAY: Remember , there is still our cold front from the Rockies that created
the early season snow. It is expected to be preceded by a prefrontal trough on Thursday with the front to follow sometime Friday. As of the last run of the GFS, that would be 
near noon on Friday. Rain shower/storm activity is expected to be quite low, or at least 
limited in strength and expected to be isolated showers mainly. The front should clear 
the state by Saturday morning and enter well south into the Caribbean during that day...making for a very pleasant weekend.

TEMPERATURES WITH FRONT: Don't even bat an eyelash. They are not expected to fall 
quite to the levels of the previous front, but it will be coolest in the same areas as was 
the case with the last front. Thus, the immediate east coast from Port Canaveral and 
South will be warmest, with mainly 50Fs expected across the peninsula in other areas. Afternoons could remain in the 80Fs. Winds will be much quicker to shift onshore as well.

SIDE NOTE: The NAM and NoGaPs models are showing for quick tropical development in 
the Northern Caribbean, with a weak low pressure area to form and race north and close to the east coast as the front moves in. For now, disregarding namely because even if so
it would have little impact beyond what has already been stated above.

BEYOND: The boundary will align across the Central Caribbean. As has been the case in 
the long range with the GFS, a bonafide' tropical system is expected to form and impact 
(this time) Jamaica. We shall see.

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