How Tropical Storm Arlene changed the weekend forecast for Florida

JACKSONVILLE, Fla. – Tropical Depression Arlene formed Friday afternoon in the Gulf of Mexico.

This development has changed the weekend forecast not just for Northeast Florida, but for the vast majority of the state.

But why the change?

Disorganized vs. Organized Systems

Meteorologists knew something was brewing in the Gulf of Mexico over the past several days.

Many computer models indicated a complex of showers and storms was likely to develop.

But the development of a tropical storm was not forecasted.

This disorganized complex was expected to float across the Florida Peninsula this weekend, bringing clouds and bands of rain to much of the region.

But with Tropical Storm Arlene now on the board, the system is expected to slide south.

This key change has everything to do with organization and steering currents.

Weaker, disorganized systems have a tendency to drift. This drifting was forecast by the computer models, which is why rain was expected across much of the state.

A tropical storm is more organized and consolidated. This organization allows the system to be steered more by mid and upper-level winds.

These winds will continue to push the tropical depression southward toward the western tip of Cuba.

With the system so far away, scattered showers are expected in South and Southwest Florida Friday and into the weekend.

The system will not have an impact on the weather in Northeast Florida, as rain chances will be based on a cold front approaching the region.

Could it reorganize?

Some early forecast models indicated the complex could organize in the Atlantic early next week.

That is now very unlikely due to the intense shear that exists in the Florida Straits and the Atlantic.

Wind shear helps keep a lid on tropical activity, and with so much shear in place, the system will not reorganize.

One small change can have a big impact on any forecast. With a more organized complex now in the Gulf, the system will feel more of the effects of the steering currents, keeping the heavy rains well away from Florida.