After a month without any tropical cyclones active, the Atlantic basin is once again starting to get more active as the climatological peak of the season gets closer. A tropical wave approaching the Lesser Antilles, which the National Hurricane Center (NHC) has designated Potential Tropical Cyclone Six, has a high chance to become the Atlantic’s next tropical storm.

As of 5:00 p.m. EDT Monday, Potential Tropical Cyclone Six was centered near 14.2°N 59.2°W, and was moving westward at about 15 mph. Maximum sustained winds were 30 knots (35 mph), with an estimated minimum pressure of 1010 mb. The NHC gives PTC Six an 80 percent chance of development, both within 48 hours and five days. The next name on the Atlantic naming list is Fred. PTC Six is gradually becoming better organized, with recent satellite images suggesting the low-level circulation is becoming better defined. An earlier ASCAT pass this morning suggested that the disturbance had an elongated and potentially not closed circulation. Regardless, the disturbance should become a tropical storm tonight or on Tuesday morning. A NOAA Hurricane Hunter aircraft is currently scheduled to investigate Six at around 8:30 a.m. EDT on Tuesday. Tropical Storm Watches have been issued for several islands in the eastern Caribbean, such as Guadeloupe, Martinique, Dominica, the U.S. Virgin Islands, Puerto Rico, and most of the eastern Dominican Republic. In the Lesser and Greater Antilles, PTC Six is likely to produce rainfall totals between 2 and 4 inches with isolated totals of greater than 6 inches.

In the short term, the environment looks relatively conducive for PTC Six. Unlike Hurricane Elsa in early July which was moving at a speed of near 30 mph, PTC Six is moving at a manageable speed of around 15 mph, so forward speed is unlikely to be a significant detrimental factor. In addition, PTC Six is currently over warm waters of around 28-29°C (82.4-84.2°F), with the SHIPS guidance expecting wind shear to remain 15 knots or less for the next 36 hours or so. The main negative factor working against PTC Six in the next 36 hours is mid-level dry air, with 700-500 mb relative humidity values of only around 55-60 percent. In about 36 hours or so, PTC Six’s circulation is likely to interact with eastern Hispaniola, which could disrupt the cyclone. The amount of disruption will depend on how far east Six tracks, as a more west track would lead to more disruption than a farther east track would since eastern Hispaniola is not as mountainous as central Hispaniola. The current NHC forecast suggests that Six will likely remain a tropical cyclone as it tracks over eastern Hispaniola. After that time, there is a lot of uncertainty with the intensity forecast. Although Six will be heading into even warmer waters and mid-level relative humidity is expected to increase, wind shear may also increase as Six tracks into the Bahamas. It is also uncertain how the potential land interaction with Hispaniola will disrupt the system. At this time, it does not appear likely PTC Six will become a hurricane, but it remains too soon to rule out the possibility.