Coastal GA/SC Rain 9-11 July

There has been an interesting (and needed) rain event over Coastal GA (Savannah) and the South Carolina Low Country the last few days. Here is the Multi Radar Multi Sensor (MRMS) 72 hour accumulation from 8am 9 July to 8am 12 July 2022:

Click to embiggen and see location labels

The gauge at the Enki office in Midtown Savannah is showing 5.99″, which is close to the MRMS estimate. Notice the very sharp gradient and the southwest-northeast line area of heavy rain running along the coast. This is caused by storm cells following roughly the same ground track during the big rain events the last few days. Saturday and Sunday night’s rain each of dropped over 2″, and 1.8″ another last night. So far in July our gauge is showing 8.08″. But compare that to the Savannah International Airport, located 8.5 miles inland, which has only had 2.15″ over the same period. For this weekend’s rain, rain totals varied from under an inch in parts of Pooler to over 6.5″ in parts of downtown, around 5.5″ midtown, 4.5 at Hunter Army Air Field, and over 5″ at Skidaway and parts of the Islands.

Rain is one of the hardest weather variables to forecast. This example shows why – sites located only a few miles apart (indeed, only a few city blocks apart) can show radically different rain totals depending on the exact track of thunderstorm cells. Winter rains (stratiform rain) tend to be more uniform. But summer rain, which is typically convective (produced by thunderstorms), can be far more localized.

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