Texas hasn't quite been as dry as the Sahara during the last seven months. But it's been close.

For the entire state, data released Monday by the National Climatic Data Center will show that last October through April was the driest such period on record. On average, Texas received less than 6 inches of rainfall.

The latest report from the U.S. Drought Monitor reflects this deepening drought, with 74 percent of the state now in at least an "extreme" drought, and 24 percent reaching "exceptional," the worst category.

"Both of these values are the highest amounts ever since the U.S. Drought Monitor started in 2000," said Victor Murphy, the climate service program manager for the southern region of the National Weather Service, based in Fort Worth.

An exceptional drought is considered an event so rare and extreme that it occurs, on average, only once every 50 or 100 years.

The drought has begun to have a dramatic effect on stream flows across the state, with many individual river gauges across Texas showing water flows in the lowest 10 percent of historical conditions, Murphy noted.

All of Harris County is in at least a severe drought, with the city of Houston receiving only about 1.5 inches of rain over the last three months — about 15 percent of its normal amount.

That's less than some parts of the Sahara receive in the same time period.

The lack of rain has created agricultural problems across the state, including in the greater Houston region.

According to the Texas AgriLife Extension Service, high winds during recent days and nights have further dried out crops and soils. Brazoria County had almost no precipitation during April, and many crops there have gotten no significant rain since planting.

There will be no immediate relief from the drought for Houston, forecasters say. In fact, temperatures could rise into the lower 90s by Sunday, with high humidity.

The first half of next week will feel just like June, only in May.

The Houston area has virtually no chance of rain until next Thursday, when a weak cold front will approach the area. The city will probably be to the south of the main storms, however.

"Periods of strong to severe thunderstorms will likely affect a large part of Central and North Texas next Tuesday and Wednesday, bringing some much-needed rain to that area," said Fred Schmude with ImpactWeather, a private forecasting company in Houston.

Unfortunately, he said, a lot of the rain will likely be associated with strong thunderstorms bringing a risk of large hail, damaging winds and tornadoes.

"Some of this instability likely will then shift eastward across a large part of Southeast Texas, possibly as far south as the Houston area, on Thursday and Friday bringing a risk of showers and thunderstorms," Schmude said.

Later in the month, he said, a strong upper-level storm system should build over the southeastern United States.

This system will likely not only bring cooler air to the Houston area, but may also bring another chance of showers and thunderstorms as instability over the Central Plains shifts southward over Texas.

eric.berger@chron.com