"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".

Friday, October 7, 2011

Increasing Wind and Rain Threat "Sometime" Over The Weekend

"The Beginning"  - Sunset on Wednesday Evening As The First Rains Move In From the East 


Out of respect for the events of late and low confidence level of future ones, today's post is an  attempt to explain in generalities  the current conditions and complexity involved with the weekend weather forecast leading into 'potentially' the first half of next week. 

CURRENT: First of two parts is the surface or near ground level weather (that which we experience first hand). High pressure has indeed  settled into the Mid-Atlantic as expected.A  Deep trough is over the Rockies making for some very early season snow fall in all locations  expected (per the photos relayed to me from my good friend who lives in Cortez, Colorado in that state's southwest corner.)  This can be seen by extracting the latest surface depiction put out by the Rapid Update Cycle (RUC) model below:

RUC of 12PM: Onshore flow along the Florida east coast with blue arrows (and shading) showing the wind is rotating around the HIGH pressure (H) center near Pennsylvania. The flow is clockwise around the high and heads north ahead of  LOW (L) pressure centered over NE Montana, which has a trough extending Southward from it. The zig zag blue is the ridge of High Pressure  axis extending from Eastern Canada to the Texas Gulf Coast.  The question marks in orange are for where or even IF a low will form during the weekend ...and whether that low, if it forms, will be a surface low or one in the mid-levels of the atmosphere....for now...the 5,000 ft level which is near the lowest of what would be considered "mid-level"  

Just to be sure, I've extracted the latest 10M (meter) plot from the LDIS (Local Data Integration System) from the MLB (Melbourne) NWS (National Weather Service) website of Florida...below:

LDIS for 10M: If you recall yesterday's plot, the color coding was all blue. Now some light greens are getting into the picture of sustained 20-25knts winds near the ground (over the waters). The purple areas are little bubble 'troughs' that are formed as the winds suddenly drop off when hitting the shore line. When joined, they form a marine/coastal trough up and down the east coast. So far as of sunrise, all or most of the rains have occurred at and west of the trough (as well as offshore). Some lightning and thunder was observed last night to early morning from JAX toward Ft. Pierce, with the heaviest and most persistent area near Ft. Pierce in St Lucie County toward Vero Beach...where rains persisted and kept reforming in the same area.

Rainfall in St. Lucie county per radar estimates and an actual COCORAHS observer were close to 5 Inches here. This could be considered a localized 'rain event'. Pointing this out, because this will be how the weather will materialize through Saturday and into Sunday. Some areas will see little to no rain, whereas other areas will or could get excessive amounts mainly at or near the coast.  Interestingly this morning, the rain in St. Lucie did not progress to the west, but stayed in the same area as it was refueled by the heat and moisture source, i.e. The Atlantic.

last night was a good example of how the weekend could unfold. The difference will be that surface winds will be stronger everywhere and there should be more pockets of rainfall, especially on late Saturday into Sunday. Just where those areas will be is very difficult to determine until a low pressure area at the surface or just above the surface materializes. At that point, we can count places out and hone in on 'target areas'.

But, now look well overhead at the jet stream level, remembering how breezy it is today from the east-northeast at ground level:

25,000 feet overhead. There is a big zig zag ridge axis in blue and the trough out west even at this level, but note the trough over Florida and the WSW winds over head (oppostive direction than the surface wind shown in the previous images). There is even a bit of a low circulation where the red "L" is drawn along the trough axis in red.

Winds will increase in 'surges' as has been the case since the pattern first began to evolve. Another surge is expected toward dusk tonight. Surges are often accompanied by increased cloud coverage and rainfall in some locations for a brief time. We could see another 'event' overnight tonight of rain as well, but just where is impossible to know.

Winds toward sunset will decrease significantly away from the coast overnight, but remain a bit elevated at the beaches tonight although not as strong as during the daylight / early evening. Another surge of diurnal nature could occur with sunrise with more showers just about anywhere as it approaches lasting through late morning. These could work across at least the spine of the state before weakening beyond that point. 

SATURDAY: Increasing winds once again as the pressure gradient kicks it up a notch, beyond even any diurnally driven 'surge' due to the increasing pressure gradient between high and low pressure . Winds at the beaches could increase to SUSTAINED 22 -28mph with gusts to 35mph. Wind in and near any rainshower or perhaps thunderstorms will be noticeably higher with  approaching activity, but could quickly wane immediately as and after a storm has passed, before coming back up to 'status quo' during the following hour.  It is possible that surface winds will barely wane, if not pick up even further along the coast from Miami toward Brevard Saturday night as rain storms continue this common theme almost anywhere along the east coast at night and less so 30 miles or more inland.

HINT: If one is outside at night and you detect the wind starting to increase but cannot see the sky, that can mean a rainstorm is either near by or about to pass over head.

SUNDAY/BEYOND: This time frame continues to remain the "Great Beyond" at this point, leaving this space to briefly recap and surmise.


ISSUE #1:  The first observation is that the ECMWF and Canadian Model, and now even the NAM of 'old unreliable fame' are coming into closer agreement to what the GFS had portrayed last Saturday when it was first mentioned here that there could be an upcoming rain event along the Florida east coast. It is now the GFS that is no longer sticking to those guns. Only the NoGAPS comes close, but it is forming a low much further to the east of the state than any others, having no impact whatsoever to the state.

ISSUE #2: The NAM is now in close agreement with the ECMWF in location of a low pressure trough and eventual 5000 ft or 850mb low toward SW Florida. Only a very weak low pressure circulation at the surface is noted, but they are quite close. And, for a change, it is the GFS that is much faster to form a low..even faster than previously thought, which runs eventually up the east coast. That is, on Saturday evening. All of the windy and wet weather in any case with a low will be north -northeast of the low. Thus, even though the GFS forms one near Miami, they remain dry..whereas further up the coast rain chances increase. But even so, the GFS has very little rain with the system over fact, even any wind. PROBLEMATIC FOR SUNDAY'S FORECAST if one is to consider this model.

ISSUE #3: Line of thinking. For now, it is probably best to run with model agreement/concurrence which would be a blend of the ECMWF (Euro for short) and the NAM (even though it has been very unreliable lately). There is another reason though. The NAM is much slower in the low pressure center evolution, and is depicting the areas of rainfall much better than the GFS. The GFS is too general, making it appear as if it will rain everywhere up and down the coast at almost the same time, whereas the NAM has a better handle on capture convergence bands and vorticity banding, and thus not showing 'rain everywhere' simultaneously. 

ISSUE 3: For consideration. If the GFS verifies, rain is pretty much over on Sunday as the low moves up the east coast (except toward Jacksonville). This is a big change from previous runs. If the line of thinking with the NAM/Euro is correct, rain chances remain elevated through Monday at least.

FINAL THOUGHTS: Watch for a mid-level low as opposed to surface low to form either right over the state or in the eastern Gulf over the weekend. This could be the dominant feature. If so, then we'll have to watch for it to 'cut off'. As noted several posts ago, cut off lows are seldom forecast with much accuracy beyond 48 hours, and none is yet shown to occur. But if so, they move slowly. 

BUT LASTLY: Inevitably, either somewhere along the east coast will get inundated with more high rain totals, and not to be left out, if the Euro comes to fruition which has not been mentioned much, the SW Coast of Florida. Both the GFS (to give it credit) and NAM increase precipitable water significantly heading into Saturday, which means heavy rains somewhere, including the Metro Areas of SE Florida.

GREAT BEYOND: In any case, no matter which model verifies heading toward Monday, there is a chance that more rainfall could be in the forecast for quite sometime after a 1-3 day break...but then again, oddly, my Accurite Weather Station forecasts for the first time in days NO rain in it's automated weather icon of a cloud with rain falling out of it and now has sunshine. Have to watch that thing and see if it has something going for it.

Wednesday Evening After the Rainbow

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