"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".

Thursday, October 6, 2011

Stronger Breezes and More Frequent/Heavier Showers To Increase This Weekend

Current Local Data Integration System (LDIS) Plot From 3pm, Thursday (today).
This surface plot shows the average 10 meter winds by the wind barbs and color coded scale to the right. Note that winds are weaker toward the interior and west side of the state. High pressure is to the north and low pressure to the south.

Taking a little time today to show graphically what is going on in the next 48-72 hours. The above zoomed in image of Florida shows in general the isobars of constant barometric air pressure aligned across the state. Note how close together they are due to how close the low and high pressures are (as well as to the strengthening high pressure). The closer together the lines, the stronger the wind. They will get much 'closer' on Saturday or Sunday. 

As mentioned in previous posts, High pressure from Canada will be added to the mix on fact, the process has just begun. But it is still building southward behind the big low that finally is departing Nova Scotia after spending nearly two weeks over the Great Lakes to the NE States. Now that the low is moving out, high pressure can move in and down the coast to replace it at all levels through the bottom 10 - 15,000 ft above (or up to 3 miles  overhead).  This can be seen by looking at the wind forecast for 20,000 feet by  Saturday morning.

High pressure arcs into Canada well aloft, and the GFS has an upper low forming West of the Fort Myers area in the SE Gulf. That trough to the west shown above will bring wintry, wet, stormy, and possibly flooding conditions to parts of the Plains states going into and through the weekend at times. Dry and pleasant weather will persist to the north of Florida where it had been unpleasant for so long last week. 

Note the potential for the upper low off the Florida West Coast. Underneath that low Southern Branch jet stream winds are  expected well overhead our state, while at the surface winds are expected to increase much more than than area today from the ENE-East. Convergence is noted along the east coast as the easterly winds collide with the coastline and converge or press/squeeze the air mass and the moisture in it. This process  induces rainfall at the coast, although most will already be coming toward the coast from well off shore. This can be seen by what is occurring today.

Convergence on the east side and divergence on the west side where the winds slacken and spread apart to a very small degree. Convergence is more suitable for heavier rain fall whereas divergence tears it apart.

The winds shown in the image above are expected to "surge" increase as more high pressure circulates out over the Atlantic from the building dome of high pressure to the north up in to Canada by Saturday morning, although they should increase more in small phases now and then at just about anytime before that time. The most notable times for diurnally driven surges are near sunrise and during peak heating, and sometimes late in the day toward sunset, with the weakest winds at night outside of rain showers.

This will be how winds will operate in coming days. Thus,during the late morning toward noon toward 6-7pm rain can cross the state but weaken beyond  20 miles inland in most cases, but as night falls instability over land decreases and showers cannot sustain themselves. On the other hand, the ocean remains a constant warm 80F+ degrees day and night, thus the most instability will be near the beaches so that off and on rain showers can continue. This is the main reason the big rainfall totals should occur near the beaches through Sunday...evening accumulations outside of external forces such as a well developed low pressure system.

Expect more weather like today on Friday, with slightly stronger winds and more rain showers. Not everyone is getting rain today, and most are not. This will be the case once again tomorrow, but some more areas should see rain at some point, with winds increasing a bit.

SATURDAY/SUNDAY: It is during this time frame that surface winds should increase even more as the opposing pressure patterns begin to butt heads most affirmatively. Neither system to the north or to the south wants to budge, and the result is a tightening pressure gradient and stronger wind, and thus more convergence at the coast and more rain with thunder possible. Winds in heavy rain showers or thunder could gust toward 40mph later on Saturday and Sunday. By Sunday the NAM and to some extent try to form a surface low near the SE Coast, but that is only one option. If it does occur, weather 'action' would increase first along the coast of SE Florida to eventually work up the east coast and worsen with time. But that is only one scenario.

BEYOND: Like before, models do not agree on IF, WHEN, HOW, WHERE, or WILL a surface low will form to further complicate matters.  'IF' one forms the weather over the state will be significantly affected. 

"WHERE" - "IF" f a low forms to far off the east coast and moves north, weather everywhere is significantly improved. The closer to the coast to on shore a low forms, the more downhill the east coast conditions will become as it moves up the coast.

IF it forms more toward the interior or off the west coast, conditions everywhere could be varied vastly but in a different way from what the weekend has to bring. 

"HOW" - Another scenario involves only a mid-level low forming over the state and stretching NE toward SW Across the state with time. This was depicted originally by the GFS a few days ago and is now what the Euro (ECMWF) model is showing today.  And as if in jest, the Canadian has two lows, one performing like the GFS but it goes into the Gulf and wraps around another one rather than moving all the way up the east coast. 

BUT IN ANY SCENARIO: WHEN? There seems to be agreement on this parameter. Later Sunday.

Thus, the future remains unknown.    If a system forms over or west of the state, rain chances continue well into next week, but the winds subside significantly. Any boundary left over in the Caribbean when all is said and done, whenever next week that might be..could induce a purely tropical system to form heading toward the last week of October.  So, more opportunities to watch the tropics still loom in the next two weeks at least. 

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