A map of the Texas Coast is projected on a screen as an emergency response co-ordinator warns of the approach of Hurricane Harvey. Picture: AP

TEXAS is in the firing line of a rapidly forming, high-intensity hurricane — predicted to be the worst for a decade.

Hurricane Harvey is likely to become the worst storm to strike the US mainland in more than a decade.

The US Weather Service is warning residents of Houston and Galveston to “prepare for life threatening rainfall flooding ... Small streams, creeks, canals, and ditches may become dangerous rivers. Flood control systems and barriers may become stressed.”

The hurricane, now about 400 kilometres south-southeast of Port O’Connor, with maximum sustained winds of 140 kilometres per hour, is likely to make landfall along the middle of the Texas coast by Friday night or early Saturday.

A shuttered local business has a sign for Hurricane Harvey. Picture: AP Photo/Eric GaySource:AP

Residents wait inside the Corpus Christi Natatorium to board a bus to evacuate to San Antonio. Picture: Courtney Sacco /Corpus Christi Caller-TimesSource:AP

Jim Gilbert boards up a window at his home in Magnolia. He and his wife plan to stay through Hurricane Harvey and watch the storm. Picture: Ana Ramirez/The Victoria Advocate via APSource:AP

Shoppers pass empty shelves along the bottled water isle in a Houston grocery store. Picture: David J. PhillipSource:AP

The weather warnings go much further than bursting river banks.

“Potential impacts in this area include: Structural damage to sturdy buildings, some with complete roof and wall failures. Complete destruction of mobile homes. Damage greatly accentuated by large airborne projectiles. Locations may be uninhabitable for weeks or months.”

And then there’s the “life-threatening (sea) surge having possible devastating impacts”. Estimates place the surge at more than 350cm.

Brownsville, Texas: residents prepare for Hurricane Harvey. Picture: APSource:AP

GROWING FAST

The urgent warnings are being issued because Hurricane Harvey is intensifying with unanticipated speed as it sits over the warm waters of the Gulf of Mexico — evolving from a mere tropical depression to a monster spewing 140km/h winds in less than 24 hours.

By the time it crosses the Texas coast, Harvey is expected to be a high-end Category 3 beast with sustained winds of up to 200km/h.

Once it crosses into Texas, weather forecasters predict it is likely to get trapped between two high pressure systems. This will cause Harvey to slow and sit virtually stationary — lashing Houston and San Antonio with heavy rains and winds for days on end.

It’s a nightmare weather scenario which could result in up to 75cm of rainfall in some areas.

The last hurricane to unleash such force on the United States was Hurricane Wilma, when it crossed over the Florida coast in 2005.

Superstorm Sandy, which pommeled New York and New Jersey in 2012, never had the high winds and had lost tropical status by the time it struck. But it was devastating without formally being called a major hurricane. “

“We’re forecasting continuing intensification right up until landfall,” National Hurricane Center spokesman Dennis Feltgen said.

Caleb Armstrong, 9, plays on the beach in Galveston, Texas as Hurricane Harvey approaches. Picture: APSource:AP

EMERGENCY RESPONSE

Authorities in southern and southeastern Texas are scrambling to prepare for the storm surges and flooding. Normally they have several days to pre-position resources, personnel and relief supplies to counter such a potentially catastrophic event.

But Harvey has simply appeared out of nowhere.

Landfall is predicted between Port O’Connor and Matagorda Bay, a 50km stretch of coastline about 110 kilometres northeast of Corpus Christi. The region is mostly farm or ranchland dotted with waterfront vacation homes and has absorbed numerous Gulf of Mexico storms for generations.

No widespread evacuations have been ordered yet. Officials in Port Aransas and Aransas Pass, two small coastal towns near the projected landfall area, asked the 12,000 residents to leave and warned those who stayed behind that no one could be guaranteed rescue.

President Donald Trump on Twitter asked people to get ready for the hurricane and posted links to websites for the Federal Emergency Management Agency, the National Hurricane Center and a Homeland Security site with tips for emergency preparedness.

Typical Category 3 storms damage small homes, topple large trees and destroy mobile homes. As in all hurricanes, the wall of water called a storm surge poses the greatest risk.

Harvey’s effect would be broad. The hurricane centre said storm surges as much as one metre could be expected as far north as Morgan City, Louisiana, some 650km away from the anticipated landfall.

A sign is displayed at JB's German Bakery & Cafe as Hurricane Harvey approaches the area in Corpus Christi, Texas. Picture: APSource:AP

PREPARING FOR THE WORST

In Houston, one of the nation’s most flood-prone cities, Bill Pennington told AP he was philosophical as he prepared his one-storey home for what he expected would be its third invasion of floodwaters in as many years and the fifth since 1983. “We know how to handle it. We’ll handle it again,” Pennington said he told his nervous nine-year-old son.

Dozens were in lines at a Corpus Christi Sam’s Club, at home improvement stores and supermarkets. The city also was passing out sandbags. Alex Garcia bought bottled water, bread and other basics in the Houston suburb of Sugar Land after dropping his daughter off at college. He said grocery items were likely more available in Houston than back home in Corpus Christi, where Garcia, a beer distributor salesman, said stores were “crazy.” “We’ll be selling lots of beer,” he laughed.

Kim Fraleigh, of Sugar Land, stocked up with five cases of water, three bags of ice and other supplies at a supermarket.

“We’ve got chips, tuna, dry salami, anything that does not require refrigeration,” she said.

Joey Garcia, director of the HEB store, said more than a semi-trailer load of water was sold Wednesday, and he expected to two more trailers on Thursday. In Galveston, where a 1900 hurricane went down as the worst in U.S. history, City Manager Brian Maxwell said he was anticipating street flooding and higher- than-normal tides.

“Obviously being on an island, everybody around here is kind of used to it.”