Tropical Storm Arthur could form near the Texas Gulf Coast by Wednesday, but even if it doesn't develop, days of heavy rain will trigger flash flooding in the South, from Texas to Louisiana, Mississippi, Alabama and Georgia.

(TRACKING MAPS: Spaghetti models, forecast winds, satellite and more)

The National Hurricane Center has issued tropical storm watches for the northwestern Gulf Coast from Sargent, Texas to Morgan City, Louisiana. This means that winds of 39 mph or higher are possible in the coming days.

The system has now been called Potential Tropical Cyclone One by the National Hurricane Center.

A potential tropical cyclone, or PTC, is a disturbance that has not yet developed into a tropical cyclone but poses the threat of bringing tropical storm conditions to land areas within 72 hours.

(EXPLAINED: What is a potential tropical cyclone?)

What about possible Arthur?

An area of low pressure is attempting to form near the Texas Gulf Coast.

If it forms offshore, it could sprout just enough showers and thunderstorms to be deemed either Tropical Depression One (if its winds are less than 39 mph) or Tropical Storm Arthur (if its winds are at least 39 mph).

Even if it does develop, it won't spend much time over the Gulf, as it should be inland over the Deep South by Thursday.

The main threat, whether or not Arthur develops at all, will be heavy rainfall.

(MORE: Atlantic hurricane season outlook update)

Where the soaking rain is now

This system is already soaking parts of the Gulf Coast. The radar map below shows where bands of heavy rain are currently soaking parts of the South, from Texas to Alabama.

We've already seen some flash flooding.

Monday, 2 to 5 inches of rain triggered flash flooding in parts of central, southern and eastern Texas into Louisiana and southern Mississippi.

Flooding of low water crossings in the Austin and San Antonio metro areas into the Texas Hill Country. Further east in Burleson County, Texas, five vehicles were stranded in high water, requiring water rescues.

Flood threat

Flood watches have been issued by the National Weather Service in areas shown by the light green polygon from coastal Texas into the Deep South, including Corpus Christi, Houston and New Orleans.

Flood threat is in play for days

If Tropical Depression One or Tropical Storm Arthur does form, it could concentrate an area of heavy rain near the Texas and southern Louisiana coasts Wednesday, then into other parts of the South Thursday into Friday as its remnants move well inland.

But, again, even if tropical development doesn't happen, a threat of heavy rain is in play over the South all this week.

Bands of locally heavy rain are possible from parts of Texas into the Tennessee Valley. Through Saturday, some areas may pick up as much as 5 to 12 inches of additional rain, with locally higher totals where bands of rain stall for a few hours or more.

This could lead to dangerous flash flooding and some river flooding increasing as the week goes on.

Stay alert for any flash flood warnings and never drive into a flooded stretch of road. Turn around, instead.

(MORE: Why you should never drive into a flooded road)

Other Impacts

Gusty winds will arrive Tuesday night on the upper Texas Coast and southwest Louisiana by Wednesday morning, possibly reaching 40 mph.

A storm surge of 2-4 feet is also possible between Port Bolivar, Texas, and Morgan City, Louisiana.

An isolated tornado is possible over the next few days along the Gulf Coast.