Tropical Storm Gabrielle is expected to strengthen into a hurricane soon as it moves west across the Atlantic, forecasters said.

Tropical Storm Gabrielle could form this week, while Mario could bring rain to Southern California in the Pacific.

The long lull in tropical activity, right at the peak of hurricane season, has flummoxed meteorologists. We talked to experts about what’s going on, and when things may change.

A tropical wave west of Africa in the Atlantic Ocean is expected to become a tropical depression or storm sometime next week, National Hurricane Center forecasters said Sunday morning. The system was producing a large area of disorganized showers and thunderstorms and moving west-northwest at about 10 to 15 mph as of 7 a.m.

“Environmental conditions are conducive for additional development, and a tropical depression or storm is likely to form in the next day or two as the system moves west-northwestward or northwestward at 10 to 15 mph over the central tropical Atlantic,” forecasters said.

Despite a few decidedly quiet periods so far, forecasters say the conditions are still favorable for more hurricanes this year. The latest storm, Gabrielle, formed on Wednesday.