"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, August 27, 2010

Early Afternoon Update For Florida Readers

(Image: Latest KSC sounding available on the net at 11am, Friday)
NOW: Included in this post is the latest KSC Sounding. Inspection of the sounding coupled with the morning model runs pretty much keeps the previous discussion on status quo. The exception is that there is pretty significant drying of the atmosphere with the PWAT having fallen from 1.97" to 1.79". Also, the 700mb temperature has gone up a degree as the low level inversion slowly erodes.  As expected, the ENE-NE winds at the surface have developed across much of the eastern half of the region, but the weaker midlevel WSW winds aloft continue but mainly over the what I'd consider to be in the upper portions of the mid-levels.
UPDATE FOR TODAY: Hence, expect no rain activity along a diffuse sea breeze boundary early in the afternoon...with a continued chance of storm development after peak heating (i.e. - after 4:00pm). From this time on storm height and coverage will increase with many areas not receiving any rain, whereas other areas will experience a brief period of very heavy rains with lightning. Unlike the earlier post, now looking at activity to once again make a late exit entirely from the area...last affecting the coastal communities as late as midnight. Orange and Seminole Counties seem to be the mostly likely areas to have the greatest rainfall totals when all is over with due to lingering activity.
SATURDAY: Looks like there could be a bit of a break in activity for Central Florida, but entirely so. In other words, no change yet in philosophy
SUNDAY: Fly in the ointment doing the breast stroke. Pattern reversal as expected with showers first coming onshore as soon as the pre-dawn hour which spread in coverage and intensity and coverage as the push toward the WSW across the spine of the state toward the west coast late in the afternoon. More showers could come on shore through the day on Sunday...but we can look more into this possibility as time goes by.
COASTAL CONCERN: Strong rip tides and high surf. Peak looks to max out on Sunday afternoon through most of Monday then be slow to wane into midweek. At time, no expecting any significant erosion for the surf.  Seas will once again pick up, maybe more so around Thursday. Erosion might be more of an issue which I'm sure the pros in the NWS are watching.

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Mid-Late Afternoon Showers and Storms Possible Again Today

(Image: Enhanced infrared satellite image shows lows in the SW Gulf and off Louisiana; Hurricane Danielle and TS Earl)
RECAP: Rains were late to get going yesterday under the canopy of mid-level clouds that just wouldn't break lose. It appears that a few things kept storms from developing robustly yesterday. Firstly, the cloud cover kept temperatures below the convective temperature during the day and also from breaking entirely the low level inversion which was referred to in yesterday morning's post. Additionally, it appears a bubble of surface high pressure developed over East Central Florida which was slow to move offshore. We also never really had a true sea breeze circulation yesterday. Granted, an easterly low level easterly flow did develop before noon time, but this really wasn't a true sea breeze. This was easily seen when considering the fact that the easterlies developed almost uniformly across the entire Central Peninsula at the same time, rather that as a 'sea breeze front' created by temperature variations between land and sea. With very light easterlies being overrun by very moist WSW-SW winds at the mid-levels the altocumulus deck was further enhanced and become self-perpetuating. By early evening the bubble high had moved well offshore coincident with an upper level vorticity max which crossed the North Central Portion of the state from west to east. As such, by early evening thunderstorms and showers were wide spread from mainly Daytona Beach northward.  As the high moved further off and lost its grip the first heavy shower over the immediate Central Portions crossed downtown Orlando. This was followed by more activity over SE Osceola and extreme Southern Brevard. Eventually a larger area of moderate showers lined up approximately 30 miles either side of a line along the Beach Line from Brevard through Orange and Seminole Counties..and points even west of these locales, while more rains continued to the north near Ocala and Gainesville in the 10-11pm time frame. Other storms were located just east-NE of Lake O in Palm Beach County. The whole kibosh has since then moved east this morning.
LOCAL SYNOPSIS: The vorticity max and associated weak surface low (well east of Jacksonville) is off shore, and a lingering line of showers and storms trails from the low SSWard to right on the coast at West Palm Beach. Meanwhile, another bubble high has formed in its wake over Central Florida. The timing has been just right to clear out the cloud deck which has been in place for a couple of days now. Additionally, the light winds and clearing skies have given way to the coolest morning we've seen across the entire northern 1/2 of the state than we've seen in maybe two months ...except the western 1/2 of the Panhandle. KSC sounding is showing similar mid and upper level temperatures to yesterday and the day before, with not surprisingly an inversion in the low levels. The inversion could be a reflection of the bubble high over the area in the wake of the 'system' that has moved off shore. The air mass is still quite moist, despite the nearly clear skies at time of writing, misleadingly so...with a convective temperature around 90-91 degrees. Sure looks stable out there right now as of 8:45am.
ELSEWHERE: As was thought a possibility, that low in the far SW Gulf referred to yesterday has become a big player. Indeed, there continues to exist an inverted trough extending from this low which is now hugging the Mexico Coast which extends NNE-NE-ENE-Eward into a developing low centered just south of Louisiana. Both lows (the one off Mexico and the other off Louisiana) are easily seen on the color enhanced infrared satellite image included with this post. This boundary continues ENE toward the old circulation over SW Georgia where it merges with what was the cold front which was moving east of the Mississippi River Valley region yesterday morning. Meanwhile, broad area of high pressure continues to build into the Mid-Atlantic Region from the west. This inverted trough (actually becoming a stationary front from the low south of Louisiana) will remain in place today with little change. The low south of Louisiana will likely strengthen further at the surface and midlevels and move west, paralleling to and just south of the Gulf Coast states...but likely bring some significant rains to the TD Landing Strip of Southern Louisiana into Mississippi/Alabama today along the stationary front extended E-ENEward from it.  Under this scheme of things, most of peninsular Florida remains in a no-man's land with a surface ridge axis extending still across the southern portion near Lake O and the mid-level axis extending from the Western Atlantic to just along or north of the Florida Straights. With all this going on, winds in the mid-levels remain from the WSW but to less a degree than the past few days.
TODAY: Believe the bubble high will push offshore during the course of the day. Very light NW winds to mostly calm winds for that matter at the majority of locales at 8am will give way to light NE-E winds by 9-10am.  A light to moderate WSW prevails aloft just above the inversion level through 20,000 ft. Without the cloud cover present today, that convective temperature of 90-91F will be reached almost anywhere today...particularly along and west of I-95. Showers could form as the easterly component wind from the eastward moving bubble high is enhanced by somewhat of sea breeze with better heating of the day. The wind should remain light and variable along the coast, then initially become NE-ENE and veer more toward the east or maybe ESE as the sea breeze develops and moves inland. Not expecting much low level convergence (showers) to form along the boundary as it develops due to the continued presence of the by-then eroding inversion. Cumulus cloud field will form between 12 -2pm in the meantime and become more enhanced throughout the day with prolonged heating. Showers could eventually start to go up in earnest in the 1:30-3:00pm time frame first along the pseudo-sea breeze front then inland as well. Once shower/storm tops grow to efficient heights while the bubble high is well out of the picture all activity should begin an E-ENE motion toward the coastal locales specifically north of Ft. Pierce.
Much further north, even though this region is closer to the stationary frontal boundary, convergence for north central Florida looks weak and remaining cloud cover should keep this area more stable. The areas most likely to receive thunder today should be roughly south of Brooksville on the West Coast to Daytona on the East Coast. Convection (and thunder and lightning producing activity) will be enhanced as it first penetrates the sea breeze front just west of I-95 from near Oak Hill to Ft. Pierce, with another area of enhancement along the eastern shore of Lake O toward West Palm possible. This area remains the 'sticky spot' due to the greater influence of the high pressure ridge nearly overhead and stronger easterly component surface winds. It will by no means rain everywhere today, and it's more likely that many areas will not get wet than will.
Unlike yesterday, shower activity should move offshore without lingering affects as was expected yesterday...with most of it gone by the 9-10pm time frame.
SATURDAY: Leaving this "in general" mode for now. The Northern Gulf surface low will retrograde westward toward the Texas Coast and pull the lingering surface boundary (stationary front) with it as high pressure becomes more of the dominating force, more notably by very late into the day or evening.  Meanwhile, winds aloft at the mid-levels will become increasingly lighter and the overall air mass will dry a smidge. Exactly how things will evolve tomorrow remains uncertain, but at time looking for a lower possibility of rain...which is less likely to be of the thunderstorm variety except over south Florida and the W-SW coast, particularly from just south of Sarasota through Ft. Myers.  Meanwhile, high pressure will strengthen with its center at the surface and mid-levels over Virginia. More of an easterly flow regime will become established by evening.
SUNDAY: Continued morphing of an easterly flow regime on this day, and watching for a mid level and to some degree a low level wind surge early in the day accompanied by low level speed convergence and resultant shower activity which would most likely affect the coast from Ft. Pierce to Jacksonville. This could continue through early portions of the day with a break during the late morning to mid-afternoon hours, then become somewhat enhanced once again later in the day as the mid-level surge moves overhead. Timing is completely sketchy as to this evolution though, and as such should be taken with a grain of sea salt.
MONDAY - THURSDAY: Easterly flow in full swing. The amount of lingering moisture is in question, but for the most part should play of little consequence for the weather across the majority of the state other than the areas along SW Florida east to the region south of Lake Okeechobee where showers and storms will remain a possibility around the periphery of the high as well as perhaps some influences of tropical nature (inverted trough).
TROPICS: Category 4 Danielle making a beautiful satellite presentation this morning as it 'eyes' Bermuda. It looks like that is all it will do though...since curvature toward the N and eventually NE before reaching this island is becoming increasingly likely. Namely due to the high pressure over Virginia which will remain in place combined with the strong upper level trough aloft and its accompanying SW-NE steering winds developing just ahead of the system.
Elsewhere, TS Earl and what looks like an errant nephew storm continue further to the east and south of Danielle and are not players until at least mid-week of next week. Earl could pose a more interesting forecast problem as we head toward Thursday as it looks now. But not so much as if it will rain, but more likely in how nice it will be here. Still, can't jump to any conclusion quite these two entities bear watching.
The big concern for these little gems will be rip currents and large surf! Swells from Danielle then stacked with those of Earl could keep the surf up for a good 10 days at least and the risk of rip currents/undertow/rip tides...however one prefers...will be highly elevated and of big concern along the entire US East Coast, especially since this activity will be picking up during the soon to be weekend time frame.

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