TODAY: Near picture perfect weather today for all but the area near and south of Lake Okeechobee with highs in the low-mid 80Fs and only a few clouds during the afternoon, if even that. The chance of more clouds increases toward Lake Okeechobee and along the east coast near Ft Pierce and south with some rain showers possible coastal Southern Dade County and through the Keys as well as coastal Monroe County toward Flamingo.
Like yesterday , the best chance of rain is for the middle keys area where Key West reported radar estimates of up to nearly 5" of rain overnight at one spot, with other areas in the middle Keys reporting 2-4", believe it or not. The chance of rain continues in these same locations through Late Afternoon Wednesday as the high pressure in the Deep South shown in the above image builds toward the mid-Atlantic and joins with even stronger high pressure the will work south from Canada behind the stubborn low pressures over the NE/New England area. More big rainfall totals could amass over the Keys during this time frame. Interesting that on the mesopage referred to in the image caption, indications exist for the possibility of a stronger storm or two over the Keys, which seems just a bit questionable today, but maybe not so debatable later on Monday.
TUESDAY/WEDNESDAY: Little change expected for South Florida with afternoon breezes, whereas further north a very gradual change is in store. Very light onshore flow is expected to develop over night tonight with slightly warmer overnight lows, especially east of I-95. Only a slight increase in clouds on Tuesday, and more so on Wednesday as deeper easterly flow develops, with the more breezy conditions coastal SE Florida. The GFS does show that some sprinkles are possible almost anywhere along the immediate east coast, but it seems more likely this will be some mostly cloudy periods along and east of I-95 at the most, and not constantly.
THURSDAY - SUNDAY NIGHT: Little change in forecast thinking from yesterday morning's post. High pressure stacks up along the Mid-Atlantic States both contributed by the Deep South as well as from the Great Lakes states once the low pressure area (The Cut off Low Pattern of MANY days now), finally is forced eastward behind departing Ophelia. This sets the stage for deeper (higher up through the atmosphere), stronger (from the surface to 10,000 ft), and more atmospherically moist ENE-E flow.
As the high pressure builds in, the rain chances end for the Keys, likely sometime late Wednesday as the frontal boundary is forced to Cuba and into a region of already lower pressures (the Caribbean). The high pressure to the north of Florida, and low pressure to the south sets up (or so it appears for several runs) yet another Blocking Pattern, the Tyrannosaurus "REX Block", named after the scientist who dubbed the pattern. But it can be a beast. This blocking pattern is most often found off the SW Coast of California in the winter months, but can occur anywhere. If so, as blocking patterns are by nature, the deep and moist onshore flow would persist across Florida and as far north as Coastal South Carolina.
With the blocking pattern in place, the next 'big trough' to enter the Pacific West Coast will be forced to Dig South rather than move from west to east as would occur in a progressive pattern. In turn, Arizona and all of the region along and west of the Rockies cools off significantly while the region east of the Rockies warms up, especially across the Northern Plains (Dakotas) and into Wisconsin and Minnesota as well as into the NE states, while Florida toward South Carolina has a good chance of rain from time to time.
Snow looks likely for parts of the Wasatch front in Eastern Utah as well as the Southern Rockies...with very cool to cold temperatures round the clock, especially toward SW Colorado due to the geography in this location at the base of the higher Rocky Mountains. Cortez, Colorado comes to mind.
This can all be seen , or envisioned, with the image below. This image was taken off the 2AM of the GFS (Global Forecast System) model. The color codes in this image are precipitation totals for the 96 hour period from Thursday night through Monday night.
ABOVE: Note the low pressure circulation centered over the Caribbean with high pressure to the north where it is rain free and warm. When this type of pattern develops and remains stuck in place, it is dubbed a REX Block. Block because it moves very little, only realigns in the same areas day after day. The trough to the west gets backed up over the Rockies, and in between the two rains add up from Texas to Nebraska. Wait, did we say rains in Drought Parched Texas??!
The colors are 96 hour rainfall totals, with the total fallen over 96 hours keyed up in the upper left hand corner where the black arrow points. As noted yesterday, the model continues to show totals up to 9" during this time frame (Thursday night - Monday evening) just off the Florida to SE Georgia Coasts. Still believe the area around West Palm to Ft Pierce will need to be watched. Again, realize this is getting far out in time, so in terms of this post, all info should be regarded as a 'heads up, you've been warned' precursory first best guess. We will have a better idea of what will actually occur heading into Tuesday evening.
As long as we're on a roll, also note the sharp drop off of the forecast rainfall once one moves toward the interior of Florida toward locations such as the west side of Orlando, other than the spurious red area shown toward Crystal River/Inverness/Cedar Key. Also note how the biggest totals are aligned in streaks associated with vorticity streamers that develop in the baroclinic zone created by the Rex Block . This was described in greater detail in yesterday's blog post. The other area of heavier rain fall in the Gulf seems to be associated with the Loop Current. And note the big totals over the Caribbean along the old frontal boundary in the zone of low pressure. This area needs to be watched for tropical development (s) well down the line into the second and third week of October.
So when does the chance of all these coastal wind convergence showers and possible thunder storms with gusty winds (in either) end? The GFS is consistent with Monday afternoon. However, as noted in the past, blocking patterns are difficult not only to determine when they will form (thus, all of the above could be incorrect if it never forms)..but also, once they do form, when they will eventually break down. Once they form, models can be easily 24-48 hours too fast (and almost always are). Thus, should it form, we could be in for the rain chances and windy conditions (which will start very late Friday) through Tuesday.
BEYOND REX: The GFS is consistent with a trough of low pressure forming across Central Florida as the block breaks, with a subtropical low or two (and who knows, maybe more) moving across the state from the SE Gulf. Additionally, another low forms near the Central to Southwest Caribbean in which either case Jamaica is impacted initially. During that time, Florida could still be impacted by showers and thunderstorms of more diurnal nature.
One thing is certain, when the pattern breaks we'll know it in a heart beat because the easterlies will quickly wane to zero and become SW and light, with the rains ending (for good in this pattern) simultaneously.