Rio Grande Valley Dodges Bullet as Hurricane Harvey Brushes By East of Region, Aug 25 2017

Overview
Hurricane Harvey, a tropical cyclone that ultimately devastated part of the Coastal Bend north of Corpus Christi with destructive winds but will be remembered as the flood of unprecedented, biblical proportion for the Houston metropolitan region, quietly passed by the Lower Rio Grande Valley with a thankful whisper for the vast majority of the population on Friday, August 25, 2017. The heaviest rainfall - an estimated 3 to 5 inches - along with beach erosion and likely storm surge inundation - touched the northeast corner of Kenedy County as the storm moved a bit closer on its way to landfall just north of Port Aransas around 10 PM. Harvey's track took the developing eye from 80 to 90 miles east of South Padre Island to around 60 miles east of Baffin Bay from early morning through mid afternoon. Tropical Storm Warnings triggered voluntary evacuations of recreational vehicles and poorly built structures along the coast from South Padre through Port Mansfield.

On the beaches of South Padre Island through Port Mansfield, tide run-up and wave set-up brought water into the dunes, but never breached the sea wall. The steady, northwest track of Harvey allowed winds to quickly shift to the west and northwest, which held back a second high tidal surge and would soon push the tide water back into the Gulf. The strong west/northwest winds did produce wave action that briefly topped docks on the Laguna side of South Padre Island during the afternoon, but no structural flooding or damage was reported. Beach erosion was nil - in fact, most of the beach was fully exposed just 36 hours later. Aerial flights to assess and photograph tidal impacts on all Texas beaches can be found here.

Inland, the hope for welcome rainfall was never realized; event total rainfall for the populated Rio Grande Valley was less than 0.5 inch. Sustained (1 or 2 minute persistent) tropical storm force winds only occurred over the open Gulf waters and the northern Laguna Madre mainly north of Port Mansfield - generally, 35 to 45 knots. A peak gust to hurricane force (64 knots, or 74 mph) was observed briefly at NOAA Buoy 42020 about 35 miles east/northeast of Port Mansfield, just before 2 PM on the 25th. Sustained winds 20 to 30 mph with gusts to 35 mph or so were common after the center of Harvey passed northeast of the region. The rare, gusty northwest winds brought a "clean" atmosphere, which led to some beautiful mixes of deep blue sky and fair weather clouds especially by Sunday (August 27). Those same west to northwest winds, which gusted often to 30 to 35 mph by day and calmed by night, compressed the hot atmosphere into near to just over triple-digit heat for most of the Valley during the weekend; McAllen/Miller airport would continue its stretch of 100° high temperatures, reaching 75 for the calendar year by the 29th. Finally, while all of southeast and south central Texas removed the word drought from the vocabulary, abnormally dry to drought conditions intensified a bit across most of the Valley. A preliminary text report of observations of wind, rainfall, storm surge/tide, and more can be found here.

Pattern Matters
Good fortune smiled on the Rio Grande Valley - but almost as thin as the skin of an onion! For days, the players on the atmospheric field in the western Gulf included:

As the remains of Harvey awoke from the dead and came free of both the dry air and wind shear that had plagued the system all the way into the Bay of Campeche, the Florida ridge edged farther west and became just dominant enough to provide the steering currents to move the resurrected Harvey on a northwest to north/northwest direction from the central Bay of Campeche. This allowed Harvey to quickly gain latitude while threading the needle of rapid intensification over very high "octane" fuel of 2 to 3° above average Gulf waters. The tightening eye strengthened from Category 2 to Category 4 while cruising by the Lower Texas coast. The rest, of course, is catastrophic history for Texas: Harvey made landfall as a 938 mb intensifying Category 4, leveling older buildings in Rockport, then got "hung" between the competing ridges. Feeder bands of rich tropical moisture dumped two feet to 30 inches of rainfall on Houston on the 26th and 27th, followed by another 12 to 20 inches in the actual swirl around the center of a weakened but still efficient rain-producing Harvey on the 28th and 29th as the cyclone edged off of the middle Texas coast. The final catastrophic chapter will be written in time from Corpus to Beaumont, but for the Valley, the close shave reminded us just how much we walk along the fine line between peril and relief.