While Harvey has made its final landfall in the United States and will ultimately diminish over land, impact from the storm will be ongoing as new incidents of flooding and severe weather occur.
Ongoing and new flooding to threaten southern US
"Very heavy rainfall will continue as Harvey's intensity slowly diminishes," according to AccuWeather Lead Storm Warning Meteorologist Eddie Walker.
The heaviest rain and greatest risk of flooding on a regional basis will extend northeastward from near the border of Texas and Louisiana to northern Louisiana, southeastern Arkansas and northwestern Mississippi into Thursday.
Rainfall over part of the lower Mississippi Valley may reach 8 inches, and much of that may fall in 12 hours.
Catastrophic flooding will continue in Houston, where the rain has ended, and in Beaumont and Port Arthur, Texas, to Lake Charles, Louisiana, even after the rain comes to an end in the coming hours. A number of large oil refineries and chemical plants are located in Beaumont and Port Arthur area.
From 1 to 4 feet of rain has fallen in this area.
Isolated tornado risk to expand eastward
Farther east, rain and thunderstorms will organize into bands. In between the bands, the sun may appear for a time.
"The spiral bands from the diminishing storm will produce localized severe weather from parts of Louisiana and Mississippi to portions of Alabama and the Florida Panhandle through Thursday," Walker said.
"The greatest threats from these storms will be isolated tornadoes, waterspouts and brief heavy rainfall," Walker said.
Enough rain can fall in the downpours to lead to urban and low-lying area flooding on a localized basis.
Spotty downpours will extend into the southern Appalachians Wednesday night and Thursday.
As Harvey turns more to the east across the Ohio and Tennessee valleys on Friday then the mid-Atlantic states this weekend, the risk of locally heavy, gusty thunderstorms will focus over the Southeastern states.
While the threat of isolated tornadoes will be much lower this weekend, a couple of tornadoes cannot be ruled out.
New tropical systems on the horizon to be of concern for US
During this weekend and into early next week, an area of torrential rain and thunderstorms is expected to gather over the western Gulf of Mexico.
Weak steering winds may allow this potential tropical system to hover offshore or drift toward the Texas coast early next week. This scenario will be monitored closely.
Should this anticipated area of disturbed weather drift onshore, the flooding situation could be made worse in some areas as it will take days and weeks for water to recede in lieu of new rain. Some locations farther south that escaped flooding may experience problems and might also be at risk.
Elsewhere in the Atlantic, Tropical Storm Irma has developed near the Cabo Verde Islands and is projected to approach the Caribbean next week.
"The next several weeks is likely to be very busy in the Atlantic basin, not only due to the number of tropical systems likely to develop, but systems that may affect North America and the U.S.," Pastelok said.