A strong tropical wave over the southeast Bahamas is likely to become Tropical Storm Humberto over the weekend. The National Hurricane Center began issuing advisories on Potential Tropical Cyclone Nine (PTC Nine) Thursday afternoon.
Forecasters at the center have noted that uncertainty is "greater than normal", and they urge Floridians to stay informed of future forecasts because tropical-storm-force winds and rain are possible across portions of the peninsula this weekend.
There are two possible scenarios that could unfold this weekend, with two very different outcomes from the eventual track and strength of PTC Nine. The National Hurricane Center has seemingly split the difference between the two with their first "cone of uncertainty."
There are considerable differences between the most reliable models where PTC Nine will go and how strong it may get. The U.S. global model is forecasting a weaker system moving across Florida late Friday into Saturday before heading toward the central Gulf Coast Sunday evening. If this occurs, an increase in showers are expected over central and south Florida on Saturday, spreading to the Big Bend and Panhandle Saturday night into Sunday. The rain would be welcome in the Big Bend and Panhandle where some areas are experiencing moderate drought according to the NOAA Drought Monitor.
Two models run in Europe — the UKMET and ECMWF models — have made a significant change and show a stronger tropical storm forming near the Atlantic coast of Florida this weekend. If this happens, rain and gusty winds would be confined primarily to the Atlantic coast in Florida. The rain bands could reach parts of southeast Florida late Saturday and spread up east coast of the state on Sunday and Monday. In this scenario, the exact track would determine how significant the rain and wind will be. A more offshore track would result in fringe effects, while a track hugging the coast may result in heavy rain, strong winds, and beach erosion. The Florida Panhandle would receive little or no rain.
If the ECMWF and UKMET models are correct, the storm is likely to be slow-moving and at least some effects — in the form of high surf, coastal flooding and rip currents — may spread northward toward Georgia and the Carolinas toward the middle of next week. However, this is highly uncertain and subject to additional change.
The National Hurricane Center will likely issue what they call a "Potential Tropical Cyclone" advisory on the system within the next 24 hours, which will provide more clarity into their forecast leanings and possible hazards for Florida from the developing system.
Another tropical wave near the Cape Verde Islands has a chance to develop next week as it heads toward the Caribbean. The National Hurricane Center says there is a 40 percent chance a depression could form. It is far too soon to know if there will be any effects over the U.S. mainland from this tropical system. If there are any, those effects would be more than a week away.
A tropical wave moving through the southeastern Bahamas is likely to bring heavy rain and gusty winds to parts of Florida this weekend, and there is an increasing chance it will become a tropical depression or storm as it does.
The disturbance, now identified by meteorologists as Invest 95, is expected to move toward the west-northwest along the periphery of a strong high pressure ridge. This ridge has been responsible for the stretch of dry, hot weather over the Southern United States in recent days. A weakness in the ridge is expected to develop this weekend, which is key to the future development and track of Invest 95.
The official 5-day tropical outlook is provided in the section below as a point of reference.
Regardless of whether a tropical depression or storm forms, numerous downpours with gusty winds are forecast to develop, especially Friday night and Saturday over the Florida Peninsula. Depending on the track of the tropical system, the unsettled weather may also reach the Panhandle and Big Bend Saturday night or Sunday. The latest official forecast from NOAA’s Weather Prediction Center shows 1 to 3 inches of rain over parts of the state, but that is subject to change pending the track of the tropical disturbance.
The widespread rain (without anything else) would be good news for some residents of the Florida Panhandle. A moderate drought has developed in some counties over the past few weeks according to the U.S. Department of Agriculture's Drought Monitor Index.
4/4 - Either way, some rain appears to be coming. Let's hope it gets to the #BigBend or #Panhandle -- there are some areas there (near #Tallahassee and west of #Marianna) that are in a drought. #flwx #tropics pic.twitter.com/7ebDvTQ9BS— Ray Hawthorne (@ray_hawthorne) September 11, 2019
Strong westerly upper-level winds and nearby pockets of dry air are the primary reasons why the tropical wave is unlikely to develop through Thursday. However, the upper air environment is forecast to become more favorable for the tropical wave to strengthen starting Friday. An upper-level low pressure area in the eastern Gulf — which is imparting the wind shear — is forecast to weaken and move into the western Gulf. A ridge of high pressure is more likely to build over the tropical wave, reducing the wind shear. The National Hurricane Center forecast as of midday Wednesday has a 60% chance of development this weekend over the eastern Gulf of Mexico.
The forecast models have a variety of possible forecast tracks for this tropical wave. The global model suite run in the United States — called the Global Forecast System, or GFS for short — project a depression or tropical storm to head more toward the central Gulf coast. If this is correct, there would be a greater chance of rain in the Big Bend and Panhandle where pockets of moderate drought have developed according to the latest Drought Monitor. Meanwhile, the European global model — called the ECMWF — and its ensemble suite show also suggest a depression or tropical storm tracking over the far eastern Gulf. Such a path would favor more rain over the Peninsula and Big Bend areas and less over the western Florida Panhandle. These differences in the models are not uncommon, especially in the development phase of a tropical cyclone.
Specifics on the more likely path and strength of Invest 95 may not be responsibly projected until Thursday afternoon or evening. We invite you to check back in with us often as the weekend (and Invest 95) approaches.