LUBBOCK — Texas continues to grow ever drier, and new data show the state has the most land in the worst stage of drought in nearly a decade.

The good news is rain appears to be on the way to Houston. How much is still in question.

The U.S. Drought Monitor map released today shows about 18 percent of the state to be in exceptional drought, up from just more than 14 percent last week.

Central and South Texas are hardest hit and are the only regions in the U.S. in extreme and exceptional drought. Ovenlike temperatures and no appreciable rain are the culprits.

Records on the drought monitor Web site show Texas hasn't had this much land in exceptional drought since at least January 2000. The previous high was in late August 2006, when about 16 percent was in the worst dryness stage.

Meanwhile, in Houston, scattered rain and muggy heat were expected today, but heavier rain and cooler temperatures are forecast for the weekend as thunderstorms stream into the Houston area.

Today, a 30 percent chance of thunderstorms is forecast for the Houston area, but the rain will be scattered. A thunderstorm east of Houston soaked parts of the area this morning, and there were scattered storms in Brazoria County before dawn.

Rain chances increase to 40 percent by the weekend.

Most areas can expect to receive about a half inch of rainfall but some spots could see as much as three inches, said Kent Prochazka, a weather service meteorologist.

Heavy moisture from the Gulf of Mexico will help fuel the rain storms, but will also keep the air muggy, Prochazka said.

The heat index, which is how the air feels when humidity is factored, today will reach about 104 degrees.

The heat index is how hot the air feels when temperature an humidity combine.

A 30 percent chance of thunderstorms is expected Friday and Saturday, when the high temperature each day will be near triple digits under partly cloudy skies and the heat index will hover near 104 degrees.

Sunday rain chances increase to 40 percent and the high temperature will dip to 93 degrees, which is normal for this time of year.

The low will be in the mid 70s.

Rain chances drop to 20 percent early next week, but the high temperature will remain in the low 90s.

Prochazka said the storms are moving into the region as a dome of high pressure that has been parked over much of Texas for weeks moves west.

The high pressure blocked rain and other weather patterns from the region, but as it moves away, thunderstorms from the Great Plains and Gulf moisture will stream into the area.

dale.lezon@chron.com