Today is the 141st birthday of the National Weather Service. On February 9, 1870, President Ulysses Grant signed a joint resolution of Congress authorizing the Secretary of War to establish a national weather service. At that time, it was called the Division of Telegrams and Reports for the Benefit of Commerce and located under the U.S. Army Signal Service.
ESE-SE winds south of the boundary shown in the first image will veer to south then SW overnight south of where the boundary is shown to be in the second image at 7am Thursday morning. We can also see in this image that the surface low off the Louisiana coast will have moved ESE overnight.
Overnight lows a good 5-10 degrees warmer tonight over Central Florida under the clouds and developing warm and moist SW surface flow. Additionally, we'll see a area of light to moderate rain move on to the west coast around midnight which will spread east mainly across the north half of Florida (including the I-4 corridor) while it teases the Beachline sector of East Central Florida until right about sunrise. A few light spits could fall as far south as SR520 after 5AM but not any further south then there for starters.
THURSDAY POST SUNRISE: Another one of those shallow/ surface boundary days not syncing with the upper level features as with has occurred with the previous two cold fronts. A sign of a change of seasons perhaps over Florida? Broad expanse of deep moisture from the surface through up through the mid-levels will spread across Central through mid-morning and beyond. The first surface low shown in the first image off of Florida will have taken off to the northeast and strengthen as shown in the second image)...while the low that forms off the Louisiana Coast moves ESE toward Tampa Bay as also shown in the second image by sunrise. These two lows combined will form a cold front that will sink slowly south through Central Florida during the afternoon which will reach Dade County by sunset. This will be a very shallow boundary, but nonetheless is followed in its passing by a NW surface wind in the bottom few thousand feet. However, it will be outrunning all the mid-upper level support (as such, the wind at those levels will remain from the WSW well after its passage). This will create a bit of an warm-air overrunning cool surface air event for Central Florida on Thursday afternoon, especially after noon time.
The surface boundary should be placed near a Cape Canaveral to Tampa Bay line shortly after noon time (around 1pm) and then near Miami-Dade by 7pm. The weak surface low will track across Central Florida proper and exit the coast near Canaveral after 1pm...followed by a NW wind, cooler air, cloudy and wet conditions. Once it reaches the warmer waters of the Gulf Stream it will strengthen and pull off to the NE more quickly in similar fashion as the earlier weak low had done. Looks like the rain should end for Central Florida near sunset.
Thunderstorms? Very sketchy at this point. The Storm Prediction Center has all of South Central and South Florida in a risk for general thunder (some strong due to winds) tomorrow. The problem with this for Central proper (Tampa to Canaveral) is that thermal instability will be lacking due to cloud cover and the time of day the surface low will be tracking across the state (before peak heating) but it is there that the southern most extent of the strong mid-upper level winds will be. On the other hand, Southeast Florida will have more heating of the day with less cloud cover during peak heating hours (and delayed boundary passage) but no mid-upper level winds at play. So at this time, if there is going to be thunder I think it would be from near Sebastian toward Vero initially with a secondary option from near Boyton Beach to Miami Metro mid-late afternoon as the boundary crosses that area. My best guess though is that thunder near there would occur offshore over the Gulf stream where another surface low could form around sunset. Another problem for South Florida for thunder chances is that the extent of warm air over-running in the mid-levels looks like it will be more pronounced ( essentially acting as a cap)...with very low lapse rates (non-conducive for rising air currents other than at the lowest atmospheric levels).
FRIDAY: On Friday the mid-upper level trough axis' will have yet to clear Central and South Florida, lagging by a good 24-30 hours from that of the surface front. Continued moist mid level flow could keep Central and to some degree South Florida in cloud cover with a chance of a spit of rain, but at this time it looks like it will be mainly mid-level, non rain producing cloud cover. NE Coastal Florida might have to contend with a little bit of back-washing effect though, and seems to be the most likely scapegoat for a rain excuse from Ormond Beach to Jax, as does the Keys.
FRIDAY NIGHT-SATURDAY: This is where the NAM and GFS greatly diverge in regards to Central Florida, namely from North/Central Brevard County to South Tampa Bay and south. How often has Central Florida Proper been the "Great Divide" these past couple of weather events?! My heavens.
But they do agree that for the most part rain chances go to nil on Saturday with the 5000 ft trough axis having cleared. The 700mb trough (10,000ft level) timing will be critical in regard to how much sun we will see on Saturday. Its very touch and go from once again for Central Proper (Tampa Bay to Canaveral). Either the clouds clear there early morning or continue once again for another day. (in other words, Saturday could be sunny in this area or totally cloudy). Further north looks okay, but either way South Florida is still in the clouds.
SUNDAY: Much cooler air make its presence known Sunday morning-Tuesday morning under sunny skies.
BEYOND A COOL MONDAY MORNING: Regionally, this is the end of the storm system / frontal boundary bombardment for a long time over Florida, at least in regards to rain making fronts. A much more zonal flow is already developing as I write. One which tracks storms from west to east at a much more northern latitude. That is why this series of troughs at various levels will take so long to clear Florida between Thursday morning through Saturday afternoon. But once we get to Sunday it looks like we will be toying with where the location of high pressure (s) will be.
For starters, it appears it will be over the Gulf of Mexico, with a surge in high pressure from the SW (Mexico) by mid week next week which merges with the Atlantic High by next weekend. Looks like there will some days with high pressure at the surface and mid-level smack dab over Florida heading through this time next week with light, squirrelly wind directions at times, often marine influenced along A1A north of Ft Pierce. Surface reflection of any fronts to go through after Saturday appear will be more of a 'back-door' variety with little impact other than to make the temperature a little cooler than what will otherwise be a running status quo of inland lows in the mid-upper 40s and highs teasing 70-74F (after Monday). Coastal lows a bit warmer and warmer all time periods south of Ft Pierce to Naples. In essence, temperatures will run to just below normal through Tuesday, and approach normal to maybe a bit above by the weekend after this approaching one.