On Thursday afternoon, NHC began referring to the system as Potential Tropical Cyclone 1 and issued a tropical storm watch for southern portions of the east and west coasts of Florida, as well as the Florida Keys. The watch includes Miami, Sarasota, Key West, West Palm Beach and Melbourne.
A tropical storm watch was also issued for the Cuban provinces of Matanzas, Mayabeque, Havana, Artemisa, Pinar del Rio and the Isle of Youth.
Potential tropical cyclone one was 95 miles northwest of Cozumel, with maximum winds of 35 mph as it moved north at 6 mph, the NHC said in an 11 p.m. ET update.
This puts the storm on track to intensify and become a tropical storm sometime Friday afternoon, with landfall expected in southwest Florida early Saturday afternoon, NHC forecasters said.
A ‘potential tropical cyclone’ is a term that NHC developed as a way to issue watches and warnings for a storm system that is expected to develop as it approached land. Prior to this change, NHC was unable to issue watches and warnings until a tropical storm had actually developed, which limited lead time on critical warnings.
“Whether the storm organizes or not, a significant flood event is possible across south Florida and the Keys,” CNN meteorologist Chad Myers says. “It is too early to say where the heaviest rainfall will be because it isn’t even a storm yet, but models are indicating that 12 to 16 inches of rain are possible in the worst areas.”
“There is still some variability on how this system will track, but heavy precipitation capable of scattered to numerous flash flooding is certainly plausible through southern Florida and into the Keys,” the Weather Prediction Center (WPC) said Thursday morning.
They are forecasting a moderate risk — level 3 of 4 — for excessive rainfall, leading to flash flooding.
Deep tropical moisture will surge ahead of the probable storm and over South Florida throughout the day on Friday and into Saturday.
South Florida is most likely in the path
The computer forecast models are beginning to concur that a tropical storm or depression will form and hit southern Florida.
“The latest model guidance is starting to come into some agreement towards this low passing somewhere over the southern portion of the Florida peninsula during the day on Saturday,” the National Weather Service in Miami said Thursday morning.
The path matters because if it takes a more southerly route, this could keep the densely-populated areas of Southern Florida out of the severe threat that comes from the northeast side of tropical storms and hurricanes.
“Gusty winds and an isolated tornado or two will be the main severe threat on Friday and into Saturday,” the NWS in Miami said. “These details remain uncertain as it will depend on the exact track the system takes. A more southern track would place the northeast quadrant over the waters, which would be a better scenario regarding severe weather across South Florida.”
So, the path matters, even if it is just a tropical storm.
Chad Myers cautions that until NHC locates the exact center of this storm, the forecast models will have a hard time accurately predicting the path of this storm.
That information will be used in computer model runs on Thursday evening, giving a better indication of the path and potential strength of the storm.
Wednesday night, without knowing the exact center location of the storm system, the American model had 3 different low-pressure locations at the exact same time, Myers explains. “To me, this indicates that the wind shear in the area may slow the organization of the potential storm and, for now, keep it from growing rapidly.”
This system has two of the three ingredients needed to form a hurricane
For a hurricane to form, you need “warm ocean water, low wind shear and a cluster of pre-existing storms … we have 2 of the 3 right now,” says Myers.
Wind shear is the change in wind speed and direction as you move up in the sky. If it is strong — like it is right now across the Gulf of Mexico — it makes it difficult for hurricanes to form.
“We have many opposing forces here,” Myers says. “It’s like trying to accelerate your car and not realizing your emergency brake is on.”
If the brake — the wind shear — eases, there is a slim possibility this storm will intensify more than is forecast.
This is the least likely scenario, though.
Another above-average hurricane season forecast
They are forecasting an above-average year, with 14 to 21 named storms, six to 10 hurricanes and three to six major hurricanes — of Category 3 strength or greater.
There are several contributing factors that play into a “busy” hurricane season.
“We are in an active period,” said NOAA Administrator Rick Spinrad. “There are certain ingredients that drive the intensity and the frequency of hurricanes.”
This phenomenon creates cooler-than-average ocean temperatures around the equator in the Pacific and results in weather impacts around the globe.
La Niña presents favorable conditions for hurricanes in the Atlantic — in contrast to that of El Niño.
This is the highest number of named storms CSU has ever forecast for the season in June, Phil Klotzbach, author of the forecast, told CNN. In 2020, the university’s forecast center predicted 19 storms during its June release, but that number included three storms that were named before the season started.
This year, no storms have formed yet.
CNN meteorologist Gene Norman contributed to this report.