By Alex Sosnowski, AccuWeather senior meteorologist
August 25,2017, 7:14:08PM,EDT
As Harvey continues to gather strength and approach Texas, the hurricane is poised to stall and unleash life-threatening and disastrous flooding into next week.Harvey is projected make landfall along the Texas coast as a Category 4 hurricane on San Jose Island or Matagorda Island, between Port Aransas and Port O'Connor, Texas, late Friday night into early Saturday morning.
Incidents of flooding and power outages will increase through Friday night and this weekend.
Harvey will have major impact in terms of dangerous surf, beach erosion, coastal flooding and damaging winds. However, Harvey is likely to be remembered for excessive rainfall and days of flooding and gusty winds well after landfall.
The storm strengthened to a Category 3 hurricane early Friday afternoon, then to a Category 4 hurricane on Friday evening. The last hurricane to make landfall in Texas was Ike as a Category 2 on Sept. 13, 2008. Wilma, in 2005, was the last major hurricane to make landfall in the southern U.S.
A state of disaster was declared for 30 counties in Texas in advance of Harvey by Gov. Greg Abbott.
Louisiana Gov. John Bel Edwards declared a statewide state of emergency on Thursday.
The decreasing forward speed of the storm will lead to long-duration rainfall and gusty winds. Harvey will cause much worse damage from flooding and wind than would normally occur from a swift moving storm of equal magnitude.
Extreme impacts are likely from Corpus Christi to Houston and Beaumont, Texas, and perhaps as far to the east as Lake Charles, Louisiana. Moderate impacts may extend as far inland as San Antonio and Austin, Texas. Isolated impacts are likely as far to the south as Brownsville, Texas.
Some communities could be under water for days
The event may be nothing short of a flooding disaster.
"Since Harvey is forecast to stall, we expect 10-20 inches of rain over a large part of southern and eastern Texas and southwestern Louisiana into early next week," according to AccuWeather Hurricane Expert Dan Kottlowski.
At the local level from 2 to 3 feet of rain may fall.
This amount of rain will lead to widespread flooding of streets, highways, bayous, streams and major rivers.
Because of the flat terrain, some areas along the major rivers and bayous may remain flooded well after Harvey weakens or crawls away later next week.
Soon after the storm begins, roads in low-lying areas may become flooded. For those in flood-prone areas, now is the time to gather personal belongings.
Prolonged gusty winds to topple trees, lead to power outages
Since there is the potential for Harvey to stall close to the coast, the storm may retain significant strength for an extended period of time.
"If Harvey remains reasonably close to the coast, it could be classified as a tropical storm through the weekend," Kottlowski said.
"In addition to ongoing heavy rainfall, strong wind gusts and saturated ground will likely cause widespread fallen trees," according to AccuWeather Senior Meteorologist Mike Doll.
From Friday night to Saturday, gusts near and northeast of the center of landfall will range between 80 and 120 mph.
Beyond Saturday gusts between 40 and 60 mph may continue into Monday and perhaps Tuesday.
When trees fall and catch utility lines, power outages will result. Power outages will be lengthy as the storm's effects last for days. Fallen trees and power lines will block some roads. Some gas stations may not have power to run the pumps. Some refineries may have to shut down.
"If the power goes out during the storm, it could take days and perhaps a week or more for crews to get to all locations, due to lingering flooding," Doll said.
There will also be the potential for brief, spin-up tornadoes.
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"As Harvey makes landfall, the risk of tornadoes will be greatest near and northeast of the center," Kottlowski said. "Once Harvey is inland, isolated tornadoes could occur throughout the circulation of the storm."
Harvey to bring dangerous conditions, cause damage at the coast
Seas and surf along the western Gulf coast will build well ahead of Harvey's arrival.
How strong Harvey becomes prior to landfall will determine the initial magnitude of inundation and damage along the coast.
"The combination of storm surge and wave action will bring a total inundation of 6-12 feet in coastal areas and bays with the greatest inundation north of the center of landfall," Kottlowski said.
Some of the worst coastal inundation on the storm's front side may occur along Lavaca Bay, Matagorda Bay, San Antonio Bay, Copano Bay and Aransas Bay, Texas.
South of the storm track, winds blowing offshore may cause flooding on the eastern part of Laguna Madre, on Padre Island, Texas.
"Very rough seas and dangerous rip currents will occur well away from where Harvey makes landfall, including northeastern Mexico and the northern Gulf coast of the U.S."
The long-duration storm is likely to cause extensive beach erosion and raise the risk of property damage along the coast.
Impact from Harvey to reach central Gulf coast
While the magnitude of rain, wind and seas will diminish from west to east across the upper Gulf coast, there will be the risk of some damage, especially in Louisiana.
How far east Harvey meanders after initial landfall early this weekend will determine the severity of impact and potential damage.
A surge of Gulf of Mexico water and moisture along will be enough to lead to torrential downpours, gusty thunderstorms and above-normal tides.
The most likely time for heavy rain to extend east of southwestern Louisiana and impact Baton Rouge and New Orleans will be from Sunday to Tuesday.
At minimum, seas and surf will be rough from Louisiana to the Florida Panhandle into early next week.
Harvey may stay alive for days
There is a chance that Harvey meanders back over the western or northern Gulf of Mexico for a time after making landfall. Some regeneration and strengthening could occur in this case.
As a result, all interests from northeastern Mexico to the U.S. northern Gulf coast will need to monitor the progress of Harvey.
Eventually, Harvey may find a way well inland over the central or eastern U.S. as a tropical rainstorm later next week and into the Labor Day weekend.
Only if the system moves inland and stays away from the coast will the storm diminish. However, if the storm should remain over Texas until its complete demise, heavy rain may continue to fall on the state through next week.