UPDATE: The odds are increasing even more. Get the latest update here.
Odds continue to grow for a slow, sloppy storm brewing in the Gulf of Mexico to become a tropical system in the coming days.
On Wednesday, the storm — which is moving north from the coast of Belize and into the Gulf — became better defined and by 7:15 p.m. forecasters upped the chances for formation over the next five days to 70 percent from 60 percent earlier in the day.
Even if no tropical depression or storm forms, parts of South Florida already in danger of breaking monthly rainfall records could see more heavy rain.
Upper-level wind shear and proximity to the Belize coast are expected to keep the system from becoming better organized over the next two days. But as it moves north and nears the central Gulf on Friday or Saturday, slow progress over warm waters could allow the system to develop, said AccuWeather senior meteorologist Dan Kottlowski. What's not clear is whether a big enough gap occurs in the shear now helping to prevent that formation, he said.
"The problem with shear is shear can weaken over a short period of time," he said.
Wednesday night, the National Hurricane Center said the environmental conditions are looking more conducive to a storm developing as the storm drifts northward.
"Regardless of development, locally heavy rainfall is possible across western Cuba and the Cayman Islands during the next few days, and over much of Florida and the northern Gulf Coast during the weekend," the hurricane center said in the 7:15 p.m. update.
But where the worst rain from the storm will fall remains uncertain. Forecasters expect South Florida to see heavy rain, but models increasingly agree the densest plume of moisture may remain offshore, Kottlowski said.
Relentless rain over the last month has pounded much of the region. Nearly eight inches have fallen along the coast in Miami-Dade County, according to the South Florida Water Management District. Broward County's coast has received 12.24 inches, more than three times the normal amount for the month. Between Monday and Tuesday, Big Pine Key got 4.17 inches.
The wet weather stems from a late season cold blast to the north, Kottlowski said. After chilling the Northeast, the cold air settled in the upper atmosphere over the southern Gulf of Mexico, weakening circulation below.
"When you create a pattern like that, you force deep tropical moisture up from the equator," he said. "It’s not really normal. But it’s not unusual."
The lack of organization also makes the system more difficult to forecast and establish the location of the heaviest rain.
"It doesn’t mean it’s not going to rain," he said. "It just means the heaviest activity could stay off the west coast of Florida."
There's also another wrinkle: There's a chance the system could become a sub-tropical system, which is similar to a tropical system without the warm center. Such storms are capable of generating the same amount of wind and rain, Kottlowski said, but tend to have an oblong shape and produce stronger winds along the outer perimeter.
If it becomes a tropical system — the first named storm would be Alberto — it could arrive just days before the official start of the hurricane season next Friday. The system is also the season's first invest. Last year, for the first time, the hurricane center began issuing forecasts for invests located close to land to give the public and emergency managers more time to prepare. The designation does not mean a system is any more likely to form.
Since flooding is the leading cause of death linked to tropical systems, forecasters have also put more effort into warnings about rainfall this year. Hurricane Harvey led to more than 80 deaths in Texas last year after getting unprecedented rain, with a new U.S. record set at more than 60 inches.
This year, the National Oceanic and Atmospheric Administration's Weather Prediction Center plans to issue more specific rain hazard maps predicting levels of risk, although forecasters are still not able to combine flooding risks from both rain and storm surge.