They say Hurricane Harvey could remain in the area, dumping rain until the middle of next week.
On top of that, the central Texas coast is likely to see a significant storm surge – this happens when low pressure at sea “lifts” tides to a level higher than normal, up to 12ft in this case, and high winds then blow the water in land.
Image source Wikimedia
The NHC said it expected “catastrophic flooding” across the coast and in some inland areas throughout south-east Texas.
Energy companies have been evacuating staff from offshore platforms in the Gulf of Mexico.
Texan oil refineries on land are also shutting down in preparation for the storm. As a result, US fuel prices have reached a three-week high.
Joe McComb, mayor of Corpus Christi, a coastal city of more than 300,000 people, urged householders to take the warnings seriously and evacuate low-lying areas.
“I hope people will listen to forecasters when they say <<beware of flash floods>>,” he said.
“Flash floods can come quickly, and they can be deadly.”
According to the NHC, the wind speed is currently almost 110mph, though gusts are even stronger.
Worldwide, the number of intense tropical storms has increased 80%, according to an article published by Science magazine in 2005.
According to recent studies, while the total number of hurricanes per year did not increase, the percentage of category 4 and 5 hurricanes did sharply increase during the last 35-40 years.
Most researchers agree that the warming oceans are the result of rising amounts of greenhouse gases in the atmosphere, also known as global warming. This process occurs when there are high levels of carbon dioxide in the atmosphere.
Global warming and hurricanes are linked because heat essentially is the fuel of these storms. Researchers have described hurricanes as heat engines that draw their energy upward from the warm ocean water to drive their winds; the increase in ocean temperatures is like throwing a log on a fire.
Typhoon Tip, October 1979: largest and most intense tropical cyclone ever recorded with wind speeds of 190mph, killed 99 people in its path across the Pacific, mostly in Japan
Hurricane Allen, August 1980: strongest Atlantic hurricane by wind speed, with sustained winds of 190mph, caused nearly 300 deaths in Haiti and severe damage in the US state of Texas
Bangladesh cyclone known as 02B, April 1991: at least 138,000 died and up to 10 million made homeless after a 20ft storm surge
Odisha or Paradip cyclone,October 1991: the strongest ever recorded in the northern Indian Ocean, killed about 10,000 people, mostly in India
Hurricane Katrina, August 2005: killed at least 1,836 people after striking states of Louisiana and Mississippi and was the costliest storm in history, causing $81.2 billion in damage (with wind speeds of 175mph)
Hurricane Wilma, October 2005: most intense tropical cyclone in the Atlantic basin with wind speeds of 185mph, killing 87 people on its path through the Caribbean and Gulf of Mexico
Typhoon Haiyan, November 2013: the strongest storm recorded at landfall, with one-minute sustained wind speeds of 197mph, it devastated parts of the Philippines, killing at least 6,300 people