"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".

Saturday, September 30, 2017

Risk of More Rainfall Over Swollen Tributaries Continues (Mainly North) Through Tuesday

TODAY: Latest radar animation out of Melbourne in combination with model guidance depictions  up to the mid-levels appear to support that a broad cyclonic circulation exists over Central Florida .  

This area might move a bit further north during the day as 'vorticity lobes' glide around it. The areas more likely to be in The Positive advection of that energy appears will be north of a line from Melbourne to Tampa Bay (in general).

There is a chance that some 'negative vorticity' advection will be on-going south of that line so that the risk of shower/storm coverage will be much lower in that area despite the presence of more than ample atmospheric moisture. 

At this point will only mention that all NWS Forecast Offices do see how problematic forecasting this 'messy situation' is that we have at hand today  going into Sunday.  It well could rain across the regions further south, but suspect that any rainfall there will be much more spotty in nature.

Counter-clockwise circulation 'appears' to be at play in the below radar animation from earlier this morning from Melbourne's WSR-88D radar, centered over Osceola County (up through 4AM).

For this post, will use the reasoning that an old frontal boundary that passed through the Northeast states and off the Mid-Atlantic Coast weakly extends southward from well off shore over the Atlantic and arching back south and west toward the Florida - Georgia Border. High pressure building in behind it from the north from Eastern Canada will breach well south toward this aforementioned boundary and in due time will extended its girth down the rest of the state, but that will not truly begin until around Monday and be especially 'noteworthy' in regard to the wind field as we go into Tuesday (winds increasing from the east to east-northeast).  

Hence, the period from Tuesday - Friday look much like what would typically be expected as 'fall weather' with temperatures having little more than a 10F degree diurnal variation, mainly ranging in the mid-upper 70Fs (lows) and lower-mid 80Fs (highs), depending on cloud coverage and proximity to the Atlantic Ocean. The closer to the beach one is, the less the variation in temperature will be.

The net affect is that as the high pressure builds south so to will be what remains of the 'convergence source' (ie, the frontal boundary). This would enable rain-showers to continue to advect on shore in 'random' fashion for a time, until the boundary washes out and a period of dryer air works in .
GFS guidance numerically shows rain chances all next week, but in looking at several models I question whether the depth of moisture will be sufficient for rain every day. The days least likely to see rainfall would be Wednesday and at least part of Thursday (at least on a wide-spread basis). 

The GFS then has been consistent in showing a 'Tidal Wave' of moisture approaching form the east as accompanied with deep easterly flow.

Again, heading from Today through Tuesday expecting 'most rainfall concentrations' (but not all) to be focus across the Northern Portions of the state closer to the frontal boundary.

Heading toward the Friday time frame, as the wind decreases just a bit  there is a chance that an inverted trough would develop along the western side of the Gulf Stream which would act as convergence area for heftier showers to advect on shore the east coast, mainly during the over night through early morning hours, coincident with the presence of this 'TBD approaching moisture'.

Heading to beyond the end of the week into the following weekend...a plethora of 'tropical' solutions begins again to be introduced. 

Given that this is within the 10-Day window (even an 8 Day one) the tropics will again bear watching. Though at this stage a 'strong system' is not being advertised, the GFS is showing what looks like would be a tropical storm lifting northward across the state in some fashion, whereas the latest ECMWF has a system lifting north well east of the state. Other models  imply a smorgasbord of possible 'low pressure areas' both to the west and to the east of the state heading toward next weekend and/or into the beginning of the following week.

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