A tropical storm warning has been issued for Harris, Galveston, Chambers and Liberty counties as Tropical Storm Cindy moves northwest in the Gulf of Mexico.

The warning extends from San Luis Pass to the mouth of the Pearl River in Louisiana, even as the forecast track shifted back east overnight.

Voluntary evacuations are underway on Bolivar Peninsula in Galveston County for those with medical conditions that depend on electricity.

A Red Cross shelter was opened in Crystal Beach.

The National Hurricane Center's 10 p.m. Wednesday update indicates Cindy is moving northwest at 7 mph with max sustained winds of 50 mph.

The current forecast track would bring the storm onshore near the Texas-Louisiana border early Thursday morning. NHC warns that heavy rainfall could produce flooding across portions of the northern Gulf Coast.

Some parts of the Houston area have seen rain as of Wednesday evening. KHOU 11 Chief Meteorologist David Paul says this will not be a wind event for the Houston area. The main concern is the threat of flooding should slow moving thunderstorms move through our area.

The latest models show the heaviest rain hitting north and east of the Houston area around 5 a.m. Thursday. Paul says the models also show a heavy rain band hitting the heart of Houston -- around Montrose, downtown and the Heights -- around 7 a.m. Thursday.

As a precaution, Gov. Greg Abbott activated the Texas Emergency Task Forces on Tuesday night.

RELATED: Voluntary evacuation issued for Bolivar Peninsula

HURRICANE CENTRAL: What you need to know to prepare for a storm

BE READY: KHOU 11 Hurricane & Severe Weather Preparedness Guide

LIVE BEACH CAMS: Gulf Coast cameras

The National Weather Service says residents in a Tropical Storm Watch should review evacuation routes and review their disaster supply kit. In a Tropical Storm Warning, the threat is more imminent, and residents should stand by for evacuation orders as well as check in with family and friends.

The Red Cross is on standby with shelters in Galveston, Bolivar, Vidor and Orange if needed.

The KHOU 11 weather team is closely monitoring Cindy and will keep you updated on-air and online until the threat has passed.

WATCH: Dr. Neil Frank, Chief Meteorologist David Paul forecast Tropical Storm Cindy

Here's what we know:

Many models continue to show a direct or near direct impact on the Houston area by Wednesday evening as a moderate to strong tropical storm. While there are a few model suits that show an impact in extreme east Texas of Louisiana, the vast majority now show a southeast Texas landfall near Galveston.

For that reason a Tropical Storm Watch has been extended west to include the cities of Galveston and Houston. A watch means that tropical storm conditions are possible within the next 48 hours.

It is possible that these watches could be expanded westward to include the rest of our viewing area and or upgraded to a warning Tuesday afternoon.

Will Cindy become a hurricane?

Probably not. However, there are some models that do show the upper-level wind shear weakening as the storm approaches land which would allow for additional strengthening. Due to the very unorganized nature of Cindy and it's eventual proximity to land by the time the wind shear relaxes, it is likely Cindy will not have an opportunity to strengthen much stronger than she is right now.

In fact the latest forecast out of the NHC says the maximum sustained winds won't exceed 45 mph from now until landfall Wednesday night. However that's a forecast and is subject to change. I can tell you that some models do show a fairly healthy and strong tropical storm nearing the Texas coast.

The image above is courtesy of the University of Wisconsin. In simplest terms the red areas are bad for development chances and green areas are very favorable for development.

What you're looking at are the upper-level winds (shear). Hurricanes require a very relaxed atmosphere with calm winds above. A hurricane needs to be what we call "vertically stacked." That can only happen when the winds are blowing slowly; generally less than 10 knots. However the analysis above is showing 60 knots sheer! Those are screaming winds!

That's the reason why Cindy looks more like a kidney bean than the more typical spinning pinwheel of a well defined hurricane. The winds are blowing the tops of the thunderstorms away from the center of circulation. Until the winds relax, which likely won't happen due to an upper-level low near Texas, this will not become a hurricane. Expect a very ugly, lopsided, water-loaded tropical storm in the central gulf.

So where's this thing going?

Areas of low pressure (tropical storms and hurricanes) always follow the path of least resistance. In this case, the least resistance path is somewhere between southeast Texas and southwest Louisiana. Many models, including the Euro model show a direct impact on the Houston/Galveston area. Other models show Beaumont while others still show southwest Louisiana.

The CMC model has been by far the most consistent with showing a landfall along the north gulf coast for well over a week. It has bounced back and forth between Houston and central Louisiana and continues to call for a landfall in southwest Louisiana.

The spaghetti models above are a conglomeration of many models showing the potential path of a tropical storm. Notice the consensus is the mouth of the Sabine River.

What can we expect in Houston?

Just because a "hurricane" is not in the forecast doesn't mean it can't be just as damaging or deadly. Tropical storms are prolific rainmakers and in a flood-prone city like Houston, this system certainly warrants your attention.

If the storm makes landfall east of Houston near Beaumont, our area will be spared the brunt of any bad weather. That's not to say that a few rain bands won't be possible. The main impacts will be well east into Louisiana.

If the storm moves further west and makes landfall on Galveston Island as some models suggest then our forecast becomes more challenging. The main impacts still will be east of the Houston area but the flood threat becomes much more tantamount. Along and east of the center of circulation 5 to 10 inches of rain will be possible with isolated higher amounts. Therefore where the center arrives will determine who gets the worst impacts.

Remember, the further west the storm hits the worse off Houston will be. The further east the better.

Cindy never was and likely will never be a wind event. However gusty winds in excess of 30 to 40 mph will be possible along the coastal counties and areas near the bay. Winds may gust to 50 mph or stronger but it'll be isolated in nature.

This is NOT a wind event for the city of Houston.

Of course the "what to expect" is ever changing with the forecast.