The water vapor imagery which shows us where we can find moisture in the mid to upper levels of the atmosphere, shows that our upper air is very soggy, almost like a sponge saturated with water. Any little squeeze and all that rain could come down. The green represents the moisture and the orange indicates areas of dry air.
Most of the time our models are pretty much in agreement and the forecast is rather straight forward, but that is not the case this time.
The following are 2 scenarios that shows how strong upper winds can be the difference between deluge and summer-like rain.
Notice the red arrows, they represent strong upper winds moving from SW to NE. Behind those strong winds is dry air.
To our South there is a small disturbance loaded with moisture.
To our east high pressure is trapping the moisture over the region. In this scenario, the strong upper winds don't move much allowing all that moisture to arrive as early as the overnight hours and drenching us.
In this case, the strong upper winds move a few hundred miles to the East pushing most of the rain into the Bahamas. This does not mean we will be completely dry, but it will send the tropical downpours east into the Western Atlantic.
The National Weather Service believes scenario #1 will be the likeliest scenario. Here is their late Tuesday night update:
TONIGHT: THUNDERSTORMS: SCATTERED THUNDERSTORMS ARE EXPECTED LATER TONIGHT AND AFFECT MAINLY SOUTHEAST FLORIDA AND THE ATLANTIC AND GULF OF MEXICO WATERS, WITH LESSER COVERAGE ACROSS INTERIOR AND SOUTHWEST FLORIDA. MAIN CONCERNS WITH THESE STORMS WILL LOCALLY HEAVY RAINFALL, GUSTY WINDS AND OCCASIONAL TO FREQUENT LIGHTNING STRIKES. OVERNIGHT THE MOST LIKELY SCENARIO IS FOR HEAVY STORMS TO REMAIN OFFSHORE THE ATLANTIC AND GULF COASTS, BUT THERE IS THE POTENTIAL FOR HEAVY RAINS TO IMPACT COASTAL SECTIONS OF SOUTHERN FLORIDA AND WITH THAT THE CONCERN FOR LOCALIZED FLOODING. GUSTY WINDS ALONG WITH OCCASIONAL LIGHTNING STRIKES ARE SECONDARY CONCERNS. STAY TUNED FOR THE LATEST INFORMATION. WIND: THE STRONGEST STORMS WILL BE CAPABLE OF PRODUCING WIND GUSTS IN EXCESS OF 40 MPH WITH ANY STORMS THIS EVENING AND OVERNIGHT. FLOODING: HEAVY RAIN IS THE MAIN CONCERN ACROSS MAINLAND SOUTH FLORIDA OVERNIGHT, PRIMARILY COASTAL SECTIONS, WHERE POTENTIAL IMPACTS INCLUDE STREET FLOODING. WATERSPOUTS: THERE IS A SLIGHT RISK OF WATERSPOUTS FOR THE GULF AND ATLANTIC WATERS. RIP CURRENTS: THERE IS A SLIGHT RISK OF RIP CURRENTS AT THE BEACHES ALONG BOTH COASTS. FROM THURSDAY TO MONDAY: CHANCES FOR THUNDERSTORMS WILL REMAIN THROUGH THE SECOND HALF OF THE WEEK. THE PRIMARY THREATS WITH THESE THUNDERSTORMS WILL BE CLOUD TO GROUND LIGHTNING, GUSTY WINDS, AND SMALL HAIL. AT THIS TIME TRENDS CONTINUE TO INDICATE THE POTENTIAL OF HEAVY RAIN AND LOCALIZED FLOODING ACROSS MUCH OF MAINLAND SOUTH FLORIDA THROUGH THE WEEKEND.