Up to 12 inches of rain is expected in Southeast Florida

A confluence of storm systems developing in the Gulf of Mexico and off the east coast of Florida would produce a consistent pattern of heavy rainfall in the Miami area Wednesday through Thursday, which could lead to flash flooding, possibly worsened by the high tide.

There is a moderate risk of widespread heavy rainfall of four to eight inches, which could lead to flash flooding from the Florida Keys through Miami and Fort Lauderdale to Boynton Beach. The computer forecast models show significant rainfall possible within the boundaries of the Keys on Wednesday morning, extending north in the afternoon. This is reported by the weather forecast center.

Some uncertainty in the forecast

Although rain was imminent Wednesday morning, forecasters at the National Weather Service in Miami said there was still some uncertainty about the timing of the heaviest precipitation and the exact placement of the highest amounts. It depends on how quickly the storm system develops off the southeastern coast of Florida, but the best indication is that the bulk of the rainfall will fall from Wednesday afternoon through early Thursday morning.

Despite these anomalies, forecasters at the Weather Prediction Center say the models show a solid 90 percent probability of two inches of rain or more across the Upper Keys in a zone stretching from Homestead to Miami, giving them confidence that the heavy rain will fall.

High tides and saturated bottoms can make matters worse.

Much of this region already has saturated soils from recent rainfall, especially in Broward and southern Palm Beach Counties, which saw two to six inches of rain on Tuesday. The soil acts like a sponge: if you keep adding water to it, eventually the soil can no longer hold it.

It all depends on timing, Weather Bureau forecasters said, but if some coastal communities also experience heavy rain around periods of high tide, the water will have difficulty receding. The tides are not relatively as high as they were when the king tides peaked last month, but with the new moon and a strong onshore wind they will be fairly high on Wednesday.

When will it end?

This will most likely only take 24 hours. As the storm system moves through the area and along the coast, the situation should ease by Thursday evening. Conditions should gradually improve with drier air filtering into cooler air moving through the region.

It was too early Wednesday morning to tell whether the system will bring significant rain along the East Coast in the coming days as it moves north.