Stocks closed the trading day narrowly mixed on Monday, Aug. 28, as insurance and energy industries grappled with the fallout of Tropical Storm Harvey's devastation in and around Houston.

The Dow Jones Industrial Average was down 7 points, or 0.04%, and the S&P 500 rose 0.04%. The Nasdaq rose 0.28%.

The Nasdaq index was buoyed by a strong tech performance, particularly in mega-cap components, and strong healthcare performance, led by biotech M&A. The Dow was weighed by insurance giant component Travelers Cos. Inc. (TRV) , which slipped 2.6% by Monday's close as insurers scrambled to assess damages from Harvey. At the same time, volatile energy markets responded to catastrophic destruction along the Texas coast.

Harvey has caused massive, unprecedented flooding in Corpus Christi, Texas, and Houston, and the storm's impact on the area's refineries, pipelines and storage remains unknown though there is evidence of major losses.

The relentless rain from Harvey, which was downgraded to a tropical storm Sunday, brought as many as 50 inches of rain. Ahead of the hurricane, refiners shut down about 900,000 barrels per day of capacity, mostly in the Corpus Christi area. Before the Category 4 hurricane made landfall with winds of 130 miles per hour, the four refineries owned by Valero Energy Corp. (VLO) and Citgo Petroleum and Flint Hill Resources shut down production on Thursday.

Exxon Mobil Corp. (XOM) closed its Baytown refinery, located on the Houston Ship Channel, when floodwaters paralyzed large portions of the area after Harvey was downgraded, according to the Journal. Exxon stock was down 0.35% Monday. The plant is the second-largest refinery in the country, processing as much as 560,000 barrels of oil a day.

Royal Dutch Shell Corp. (RDS.A) also shut down its Deer Park refinery. Shares closed lower.

The Wall Street Journal reported that Harvey knocked almost 15% of U.S. refinery capacity out of commission, which could boost fuel prices across the U.S. Gasoline futures spiked as high as 5% on Monday before erasing some gains to trade up around 2% by the close. Futures for West Texas Intermediate crude oil for October delivery settled down 2.7% to $46.57.

Shares of Allstate Corp. (ALL) , which is the second-biggest insurer in Texas, fell 1.5% on Monday.

Insurer Hanover Re is expecting total damages from Tropical Storm Harvey to fall below the levels of Hurricanes Katrina and Sandy. However, insurance research group the Insurance Information Institute told Fox Business that flood damage alone from the storm could match the $15 billion in damage it estimated Katrina caused. Sandy, which hit the Northeast in 2012, was responsible for $36 billion in damage while Katrina, which hit the Gulf Coast in 2005, caused damages topping $80 billion, according to Hanover.

United Continental Holdings Inc. (UAL) had previously hoped to resume flying out of its Houston hub Monday evening, but the Federal Aviation Administration said flights in the area aren't likely to resume until Wednesday.

Home-improvement retailers Home Depot Inc. (HD) and Lowe's Cos. (LOW)  both finished Monday trading up.

President Donald Trump will travel to Texas on Tuesday to review the state's recovery program following the storm. It's unclear where the president will visit, but Press Secretary Sarah Huckabee Sanders said the administration is still coordinating details and logistics with Texas officials.

Biopharmaceutical company Gilead Sciences Inc. (GILD) agreed to buy Kite Pharma Inc.  (KITE) for about $11 billion in cash. Kite has made waves in the drug industry for a promising new technology that harnesses the body's immune system to fight cancer.

Gilead will pay $180 a share, offering a 29% premium to Kite's Friday closing price. The deal is expected to close in the fourth quarter of this year. Gilead stock traded up 1.3% Monday while Kite shares surged 28% by the close.

Another notable Nasdaq gainer was semiconductor company IXYS Corp. (IXYS) , which announced Monday that it would be acquired by Littlefuse Inc. (LFUS) . IXYS stock jumped almost 40% by Monday's closing bell on news of the $750 million deal. The deal is expected to generate $30 million of annualized cost savings in the first two years.

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