This means tropical storm force winds of 39 mph or greater are possible within 48 hours.
A subtropical storm has characteristics of both a tropical and non-tropical storm.
A subtropical storm has a less defined and cooler center than a tropical storm, and its strongest winds are found farther from its center.
This incarnation of Alberto had the decency to wait and form after the official start of the hurricane season, but then wasted that goodwill by making landfall in Florida.
Dan Kottlowski, hurricane expert for AccuWeather, said he expects the weather system to turn into a named storm by the weekend. This could lead to flash flooding across the area. It's expected to gradually strengthen over the next three days as it begins to move to the north.
A tropical storm watch was issued Friday for the northern Gulf Coast from Indian Pass, Florida westward to the metropolitan New Orleans, as well as for Mexico, from popular cruise destination Tulum to Cabo Catoche.
Here is a historical plot of some of the systems that became tropical storms before June 1.
It's called a "subtropical storm" because it's something of a hybrid between a nontropical low-pressure area and a classic tropical storm.
Parts of South Florida could be put under a flood watch during the weekend because the ground is already saturated from recent rainfall and more tropical moisture is expected, the Sun Sentinel reported. The threat for heavy rain will reach north into the Carolinas and Tennessee.
While the storm continues to move towards the coast, its effects will take a bit of time to arrive.
The system will also create hazardous conditions along the coast.
"Its mostly looking like a heavy rain event", National Weather Service meteorologist John McMichael said.
Some areas under the heavier bands could receive up even more.