National Weather Service Weather Forecast Office

An unusually long period of warm, humid, windy weather began on Thursday, April 24th, and is expected to continue until at least April 29th, and perhaps right into the first weekend of May. Days will feature southeast winds 20 to 35 mph with occasional gusts to 40 mph between Highway 281 in eastern Hidalgo and Brooks County through the Laguna Madre, and 15 to 25 mph with some higher gusts from western Hidalgo through Starr, Zapata, and Jim Hogg County. Nights will be warm and rather muggy, with continued fresh breezes, especially near the coast. Average temperatures through the period will be 5 degrees above normal.

Impacts
The persistent winds and increasing seas and waves will maintain a high threat for dangerous longshore and perhaps some rip currents through the entire weekend and into the following week. Local and visiting beach goers beating the heat inland should use utmost caution if and when entering the surf. Inexperienced swimmers should only go into the surf to knee height, and others should be acutely aware of the longshore current, which has been known to take lives for persons not taking precautions. Boaters will see roughening seas with long period swells; those venturing on the Laguna Madre will face occasional 30 knot gusts and waves 2 feet or higher in the center channel between South Padre Island and the Port Isabel Laguna Vista area.

Farther inland, despite increasing relative humidity, there remains a threat for rapid wild fire growth. Drought stressed fuels will likely remain in the critically dry range for some time to come, and wind gusts to 30 mph can allow any fires to quickly get out of control. Burn bans remain in effect for nearly all counties in Deep South Texas; check with local officials for additional details.

Reasons
While occasionally strong gusty southeasterly winds are a staple of late winter and spring in the Valley, due to weather contrasts between the relatively close Sierra Madre Oriental and the still cool western Gulf waters (compared with rising air temperatures on land), the spring of 2009 has seen more frequency in these winds, partly due to La Niña, which has finally faded out. This latest episode will be driven by a nearly stationary atmospheric pattern, also known as a "blocking" pattern, which will lock in a strong surface high pressure system over the Mid Atlantic Region toward the Southeast U.S. coast, while a persistent, fairly strong trough of low pressure moves little from eastern Colorado and western Kansas south through West and Southwest Texas (below).

The result will be up to a week, or more, of speedier than normal southeast winds and a building swell, surf, and high seas driven by a long fetch of southeast flow between the pressure systems (below). Driving the surface weather features will be a similarly stationary upper level ridge of high pressure, initially across the entire Eastern Seaboard, then fading to the Southeast U.S. early the week of April 26th, while a general upper level low pressure trough extends from the Southwest U.S. through the western Great Plains.