(CIRA/RAMMB)

It’s hard to tell in the satellite image above, but Tropical Depression Four — which formed Thursday and dissipated by Friday evening — is still lurking over the warm waters north of Puerto Rico. It’s not strong enough to be anything more than a cluster of thunderstorms at this point, but the area of low pressure that was once a depression is still tracking west toward the Gulf of Mexico.

Although the odds are slim that this thing will become a tropical cyclone again, it looks as if it will probably be a weather-maker for South Florida by the end of the week. Most of the forecast models are keeping this system disorganized and weak, but it’s the middle of July, so even frail disturbances are worth watching if they’re heading toward the U.S. coast.

Environmental factors, such as wind shear and ocean temperature, are actually more favorable for this system now than they were last week, but dry air continues to work its way into the circulation. Tropical cyclones need warm, moist air to thrive, and dry air can prevent them from strengthening.

It is expected to maintain a west-northwest trajectory for the next several days, bringing rain and thunderstorms along the Bahamas this week, then South Florida for Thursday into Friday — then it enters the Gulf of Mexico by the weekend.


Seven-day rainfall forecast. The swath in Florida is mostly due to the remnants of TD4. (NOAA/WPC)

None of the models indicate much intensification, but the European model is forecasting what we think is the most likely situation: a weak low passing over South Florida on Thursday-Friday, then a turn toward the northern gulf coast over the weekend, with a possible “landfall” by Sunday or Monday.


Forecast of surface pressure and low-level wind spanning one to eight days. (Tropical Tidbits)

We will continue to monitor it for signs of tropical development. The next name on the list is still Don.