CABO SAN LUCAS, Mexico (CNN) -- A "dangerous" Hurricane Jimena bore down Tuesday on the Mexican peninsula of Baja California, with the resort town of Cabo San Lucas lying in its path. Meanwhile, a new tropical storm was forming in the Atlantic Ocean.
A NOAA satellite image shows Hurricane Jimena off the coast of Baja California, Mexico, on Tuesday morning.
Jimena's maximum wind speed dropped from 145 mph to 135 mph, but it still remained a Category 4 storm, according to the U.S. National Weather Service's 11 a.m. PT (2 p.m. ET) update.
"Some fluctuations in strength are likely today and gradual weakening is forecast on Wednesday," the weather service said. "However, Jimena is expected to remain a major hurricane until landfall."
Also on Tuesday, Tropical Storm Erika formed in the Atlantic, 390 miles east of the Leeward Islands, the National Hurricane Center said.
Jimena's storm center is forecast to come ashore on Thursday morning, but the weather service warned that "because it will be moving parallel to the coastline, any slight change in direction could have a huge impact in the location and timing of landfall."
Mexico's government extended a hurricane warning for most of the southern half of Baja California -- from Punta Abreojos on the peninsula's west coast to Mulege on its east coast, according to the National Weather Service.
A hurricane warning means hurricane conditions are expected within the warning area in the next 24 hours and people should quickly prepare "to protect life and property."
"A dangerous storm surge along with battering waves will produce significant coastal flooding along the Baja California Peninsula," NWS said in its 11 a.m. PT report
On its current track, Jimena's center will approach the peninsula's southern portion later on Tuesday and central Baja California peninsula by Thursday, the weather service said at 11 a.m. PT.
In addition to damaging winds, the storm could bring as much as 15 inches of rain, forecasters said.
Jimena -- the 10th named storm of the Pacific season -- was centered about 110 miles (175 km) south-southwest of Cabo San Lucas, according to the weather service. It was traveling north-northwest near 12 mph (19 kph).
People in his town of Los Cabos, at the very tip of the peninsula, were preparing for the storm and were getting a precursor as winds and rains began to pick up, said resident Cuauhtemoc Morgan on Monday.
Morgan, who sent videos to to CNN's iReport, said residents had protected every home in his neighborhood, fortifying windows with masking tape. Lines at supermarkets were long with worried residents preparing for the storms, Morgan said.
Authorities were setting up shelters in schools and trying to devise a plan to protect the homeless, he added.