The remnant of what was once Tropical Storm Harvey will redevelop in the Gulf of Mexico.
It will then track toward the Texas Gulf Coast by Friday.
Harvey may strengthen to a tropical storm or hurricane before landfall.
Harvey may then stall or meander for a few days, leading to a dangerous flood threat in parts of Texas and Louisiana.
The remnants of what was once Tropical Storm Harvey will become a tropical storm or hurricane in the Gulf of Mexico and will bring dangerous flooding rain to areas near the Texas and Louisiana Gulf Coast into the weekend or early next week.
Right now, clusters of showers and thunderstorms in the southwestern Gulf of Mexico are becoming more organized, and at least a tropical depression appears to be forming.
An analysis from the University of Wisconsin shows there is some modest westerly wind shear over the remnants thanks to a separate upper-level low pressure system off the Louisiana coast, but that doesn’t seem to be a big inhibiting factor.
Water Vapor Satellite Image
Various NOAA aircraft reconnaissance missions will provide data that, hopefully, will help numerical forecast models. The U.S. Air Force Reserve Hurricane Hunters are flying into the system today, as well.
A crucial first step to help the forecast will be to actually locate a center of surface low pressure that forecast guidance can key off of. Once that is done, Harvey will officially be resurrected as either a tropical depression or storm, depending on wind speed.
Harvey is then expected to gain strength and will draw near, if not make landfall, somewhere along the Texas Gulf Coast Friday afternoon or Friday night.
Ensemble Forecast Tracks
With an otherwise favorable environment that includes deep, warm Gulf of Mexico water, we can’t yet rule out Harvey reaching hurricane strength before its landfall, bringing the risk of storm surge flooding, high surf with battering waves and strong winds.
Rainfall Flood Danger
Harvey is then expected to be caught in a zone of light steering winds aloft this weekend that will slow or stall the circulation.
Harvey may be wedged between two areas of high pressure aloft, one over the Desert Southwest and a weaker one over the central Gulf of Mexico. Meteorologists call this zone between two areas of high pressure aloft a col.
Potential upper-level steering pattern this weekend that may stall Harvey for some time near or over the western Gulf Coast.
A tropical cyclone’s rainfall potential is a function of its forward speed, not its intensity.
Therefore, if Harvey stalls for a period of a few days, it has the potential for producing prolific rainfall, capable of major flash flooding.
It is too soon to determine the areas of heaviest rain. That will depend on Harvey’s exact path, locations of rainbands, and how long it stalls. Generally, areas along and east of Harvey’s path are in the greatest threat of flooding rainfall.
For now, areas near the Texas and Louisiana Gulf Coasts are in the biggest threat for torrential rainfall and major flash flooding, potentially including Houston and Corpus Christi.
Among the biggest uncertainties is the heavy rain potential in central Texas, including for the flood-prone cities of Austin and San Antonio. That all depends on how far inland and to the west Harvey tracks.
Rainfall Outlook Through Sunday
Harvey may still linger over parts of the western Gulf Coast into early next week before it finally moves east. This could spread additional heavy rainfall into parts of the Lower Mississippi Valley.
There are even scenarios where Harvey either stalls just off the Gulf Coast or moves back over the Gulf of Mexico at some point after having made landfall, which could allow it to restrengthen for a brief time.
The ground is already quite saturated in many of these areas from what has been one of the wettest starts to August on record.
Long-Lived Surge, Wind Threats
Harvey’s slow movement will also likely lead to additional long-lived impacts from wind.
To the east of Harvey’s center, a persistent fetch of south to southeast winds will build swells over the western Gulf of Mexico. As Harvey strengthens, coastal flooding could increase along parts of the Texas and Louisiana coasts as soon as late Thursday, then should peak Friday with Harvey’s intensification and landfall.
Given Harvey’s expected slow crawl near the coast, this coastal flooding, with battering waves, could persist in some form through Sunday, if not longer, to the east of the circulation.
Coastal Flood, Waves, Wind Setup
This water rise near the coast may not allow rain-swollen rivers and bayous to drain, compounding the inland flood threat.
Furthermore, persistent winds, even if not particularly high-end, could down more trees than they otherwise would given the rain-soaked or flooded ground.
Now is a good time to make sure you have a plan in case of both a hurricane strike and flooding. The Federal Alliance for Safe Homes can help you plan for a hurricane. NOAA also has excellent resources to plan for flooding.
Check back with weather.com for updates in the days ahead on these latest systems and the rest of hurricane season.
Source: The Weather Channel/ Jon Erdman
Photo: Super Screamer