Typically, severe thunderstorms will develop in the warm, moist airmass ahead of the storm system, and can produce tornadoes. Tornadoes can result from isolated thunderstorms or as part of a large squall line that forms along a cold front. In a thunderstorm, the tornado begins as a circulation several thousand feet above the ground, and slowly descends to the ground. Texas averages 137 tornadoes each year, the highest number of any state in the U.S. Tornadoes are most common during the spring and summer months nationwide, but due to our proximity to the Gulf of Mexico as a moisture source, tornadoes can occur in southeast Texas any time of year. In fact, some of the worst tornado outbreaks on record in southeast Texas have actually occurred in the late fall and winter months.
Waterspouts are weak tornadoes that form over water.
Along the upper Texas coast they are most common during the morning hours of the summer months, and do not require a thunderstorm to be present to form. Usually, waterspouts are short-lived, do little if any damage, and have winds well under 100 mph. On rare occasions, they can move inland as tornadoes and cause damage. Usually, they will cause only spotty minor damage, such as downing trees or power lines. Strong tornadoes are those classified as F2 or F3, with winds of 110 to 205 mph.