The Atlantic’s eighteenth named storm of the 2021 Atlantic hurricane season, Tropical Storm Sam, formed over the central tropical Atlantic on Thursday morning. Sam is in a very favorable environment for intensification and is likely to become a major hurricane in a few days. It remains too soon to tell if Sam will affect any land areas. Sam is the second-earliest eighteenth named storm on record in the Atlantic, surpassing Hurricane Rita of 2005 and behind only Hurricane Sally of last year.

As of 5:00 p.m. EDT Thursday, Tropical Storm Sam was centered near 11.1°N 39.7°W, and was moving westward at about 16 mph. Maximum sustained winds were 50 knots (60 mph), with an estimated minimum pressure of 1000 mb. Sam should turn more to the west-northwest tonight, and then move slowly west-northwestward for the next few days. On Sunday or Monday, Sam could turn a bit more to the northwest. Most of the model guidance suggests that Sam will pass north of the Leeward Islands, but interests in these islands should closely monitor the progress of Sam for potential changes. Based on the 18z SHIPS guidance, Sam is expected to be located in an environment with sea surface temperatures warmer than 28°C (82.4°F) with vertical wind shear of less than 10 knots for the next four days. This favors steady, if not rapid, intensification during that time period, and most of the intensity guidance brings Sam to major hurricane strength by Sunday. The only potential factors working against intensification during that time are eyewall replacement cycles and mid-level relative humidity near 50 percent. Since the vertical shear is very low and Sam already seems to be developing an inner core, the potential dry air intrusions should not prevent significant intensification from occurring.

It remains way too early to tell if Sam will impact the continental United States. While climatology usually favors tropical cyclones forming this far east this late in the season to recurve, and much of the model guidance also shows that happening, it is too soon to definitively predict Sam’s future. There should be a clearer picture of Sam’s future in several days, but the cyclone is currently moving very slowly over the central tropical Atlantic, and is not an imminent threat.