4. Forecast Applications

Convection » Heavy Precip./Flash Floods Example 4: Tropical Islands During the Cool Season

During the cool season or transition months, tropical islands can be affected by heavy rainfall and flash floods due to upper-level troughs, cold fronts, and surface pre-frontal troughs.

In these areas, the skew-T parameters do not need to exceed the thresholds used for flash floods in the mid-latitudes because of the abundant moisture and increased probability of warm rain processes.

Sounding taken at San Juan, Puerto Rico, 0000 UTC, 22 Dec 2001

When forecasting in the tropics, examine the upper-level synoptic environment and lower-tropospheric wind direction relative to the terrain to determine where moisture convergence and lifting will be focused over a small region.

Air masses with tropical characteristics can cause flooding events even in mid-latitudes.