The Clear Lake area faces a marginal risk of excessive rainfall starting Wednesday, Sept. 30, according to the National Weather Service's Houston/Galveston office.

The NWS posted the outlook Saturday, Sept. 26, warning that an upper-level disturbance moving north and east will bring periods of heavy rain beginning Wednesday. Peak rain chances fall on Thursday, Oct. 1 and Friday, Oct. 2.

Marginal is level 1 on the NWS's four-level excessive rainfall scale, which tops out at high. Northwestern portions of the forecast area sit under a slight risk, the next level up. The rest of the Houston/Galveston region, including Friendswood, Webster, Seabrook, Nassau Bay and Clear Lake Shores, falls under the marginal designation.

That means flooding is possible but not certain.

The office's website described the setup as deeper Gulf moisture combining with a slow-moving upper-level disturbance, with rain chances extending into the weekend of Oct. 3–4. A rise in tropical moisture and greater sea breeze activity are driving the increase, the NWS said in a separate extended outlook posted Sept. 26.

The outlook matters for flood-prone parts of the Clear Lake area. During the week of Sept. 4, the NWS noted that grounds east of I-45 remained very saturated from previous rounds of rainfall, with downpour rates of 2 to 3 inches per hour possible in the heaviest storms. Whether similar saturation levels persist heading into the Sept. 30 rain is unclear.

The NWS Lake Charles office, which covers areas west of the Houston/Galveston forecast zone, flagged the same window. That office warned of potential heavy rainfall from Sept. 30 through Oct. 4, with the active weather pattern possibly increasing the risk for severe weather and flash flooding.

The NWS Houston/Galveston office, based in League City and led by Meteorologist-in-Charge Matt Moreland, said it would provide forecast updates before Wednesday. No specific rainfall totals for the Clear Lake area have been released for this event.

Residents can monitor the latest outlooks at the NWS Houston/Galveston website.