Unexpected TS Colin forms quickly over SC, Bonnie over Nicaragua but reemerging over Pacific

In general, things don’t typically happen quickly or unexpectedly in the tropics, but when they do, it’s usually in the presence of extra warm water.

Such was the case with a disturbance moving out of the tropics this week and following the warm Gulf Stream waters along the coasts of Florida, Georgia, and South Carolina. It flew under the radar – so to speak – until it showed up on our radar yesterday morning, appearing to organize just off the coast of Georgia and South Carolina.

Tropical Storm Colin vorticity
Tropical Storm Colin – MRMS Reflectivity

With pressures initially high, the National Hurricane Center gave the disturbance only a low odds of developing yesterday afternoon.

By evening, however, winds were already gusting to near 50 mph just south of Charleston, and the Hurricane Center issued a special tropical outlook just before midnight to address the organizing trend of the fast-forming system.

Although the low-pressure center was already inland west of Myrtle Beach, South Carolina, before sunrise on Saturday, it had enough organization verified by land-based wind observations to upgrade it to Tropical Storm Colin, the rather unexpected third name storm of the Atlantic hurricane season.

While the center of Colin is forecast to move northeastward just inland along the coasts of South Carolina and North Carolina today, strong upper-level winds should both prevent strengthening and keep most of the heavy rain offshore.

By Monday, short-lived Colin should unravel over the open waters of the western Atlantic.

Tropical Storm Bonnie forecast

Meanwhile, land-based radar and ongoing Hurricane Hunter missions into Tropical Storm Bonnie in the southwestern Caribbean late yesterday indicated an organizing storm on landfall along the border of Nicaragua and Costa Rica.

Thankfully, Bonnie ran out of ocean real estate for further strengthening and came ashore shortly before midnight with 50 mph winds. The storm is producing heavy rainfall through portions of Central America this morning and is expected to reemerge in the next few hours over the eastern Pacific largely intact.

Because Bonnie stayed a tropical cyclone through its quick trip over land, it will keep its name as it emerges on the Pacific side, the first storm to do so since Hurricane Otto in November of 2016. Bonnie should re-strengthen over the Pacific but stay out to sea.

The Atlantic overall will be quieting down into next week, and tropical development isn’t expected elsewhere through at least the holiday weekend.

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