Potential for La Niña Conditions This Fall
La Niña is a metrological term that refers to a cooling trend of ocean surface temperatures within the tropical zone of the Pacific Ocean in which water temperatures remain below average. Cooling is due to strong westerly winds blowing the surface warm waters towards the west, allowing the colder water below to rise to the surface. When cooling occurs, the cooler air above the surface of the water develops, and that air holds less water vapor than warmer air.
La Niña can stretch from South America to Indonesia, thus its influence on the general weather pattern across the tropical Pacific Ocean is profound, and can impact Texas and the southern portion of the United States. Unfortunately for Texas, La Niña generally produces dry, warm weather which tends to cause droughts to last longer, cover broader areas, and be more intense. See the images below that represent typical impacts across Texas and other portions of the United States.
La Niña occurs every few years as the normal cycle oscillates from El Niño to The El Niño-Southern Oscillation (ENSO) neutral condition and to the La Niña. The last La Niña occurred in 2017 – 2018, and thankfully it was weak and short. Nonetheless, we are due for another La Niña, as the last couple years our weather patterns have been directly influenced by a combination of El Niño and ENSO neutral conditions.
NOAA has predicted a good chance for La Niña development in fall 2020, lasting through summer 2021. This is not good news for the Texas Hill Country, as drought impacts have already returned to the area, and a drier and warmer than normal weather pattern due to La Niña will only worsen the drought.
That said, a La Niña pattern is more conducive to the enhancement of tropical storm and hurricane developments across the Atlantic/Caribbean and Gulf of Mexico waters, which could increase rainfall events temporarily during fall 2020 for South and Central Texas, but would quickly die off in frequency as the hurricane season ends in November.
The bottom line is that the Texas Hill Country should prepare for the likelihood of increased drought impacts beginning this fall and lasting through summer 2021 with brief reprieves, as fall and spring time rains could bring brief intermittent relief.