outlook+water: A Hurricane Season for the Record Books, 98 Percent of Texas Abnormally Dry and Drought Projected Through Spring

outlook+water: A Hurricane Season for the Record Books, 98 Percent of Texas Abnormally Dry and Drought Projected Through Spring

SUMMARY:

  • The 2020 Atlantic Hurricane Season has a record 30 named storms (so far…), beating the 2005 season’s 27 named storms.
  • Texas continues to remain mostly in drought with 98 percent of the state at least abnormally dry.
  • Seasonal indicators suggest continued drought through the spring.

I wrote this article on November 29, 2020.

If yer gonna flirt with a record, you might as well break it, yeah? Well, we did just that with the 2020 Atlantic Hurricane Season with (so far…) 30 named storms, beating the 2005 season’s 27 named storms. And we’re not done yet: as I write, an additional system just east of Africa has a 40 percent chance of forming into a tropical storm. Hurricane season proper ends at the end of November, but the latest hurricane on record formed on December 31, 1956 (with a Category 1 forming on January 4, 1938). So don’t pack your sandbags just yet…

The 2020 Atlantic Hurricane Season also produced 12 storms that made landfall in the United States, breaking the previous record of nine set in 1916. This was also the fifth consecutive season with a Category 5 storm. About 40 percent of all Category 5 hurricanes on record have occurred since 2000.

Figure 1: Tracks of all the tropical cyclones for the 2020 Atlantic Hurricane Season as of November 29, 2020 (source).

If not for the showers (and snow!) that crossed Texas in and around Thanksgiving, we’d have nothing to show for November. For that, at least, we’re thankful (The Mace Mansion received half an inch, feeding a weaning rainwater tank). Most precipitation fell along the Gulf Coast from Beaumont, through greater Houston, on down toward Corpus Christi, sometimes providing more than 5 inches (Figure 2a).

Much of the High Plains, West Texas and Far West Texas received less than a quarter of an inch (Figure 2a).  Nevertheless, almost the entire state remains below normal over the past 30 days with West Texas, Far West Texas and the Lower Rio Grande Valley at less than 10 percent of normal (Figure 2b). Most of the state is now in a rainfall deficit over the past 90 days with splotches of normal in North-Central Texas and along the Gulf Coast (Figure 2c).

Figure 2a: Inches of precipitation that fell in Texas in the 30 days before November 29, 2020 (source). Note that cooler colors indicate lower values and warmer indicate higher values.

Figure 2b: Rainfall as a percent of normal for the 30 days before November 29, 2020 (source).

Figure 2c: Rainfall as a percent of normal for the 90 days before November 29, 2020 (source).

The amount of the state under drought conditions (D1-D4) increased from 33.0 percent four weeks ago to 84.2 percent as of the 24th (Figure 3a) with a general intensifying of conditions across the state except in the High Plains, where drought eased somewhat (Figure 3b). There are now three large areas of exceptional drought conditions: one in the Southern High Plains, one in the Big Bend area and another centered on Zavala County (Figure 3a). In all, 98.1 percent of the state is abnormally dry or worse (D0-D4; Figure 3a), up from 62 percent four weeks ago.

Figure 3a: Drought conditions in Texas according to the U.S. Drought Monitor (as of November 24, 2020; source).

Figure 3b: Changes in the U.S. Drought Monitor for Texas between October 27, 2020 and November 24, 2020 (source).

The North American Drought Monitor for September continues to show a large regional drought that stretches from Pacific Northwest down through Texas and into Mexico with short-term and long-term effects (Figure 4a). Precipitation in much of the Rio Grande watershed in Colorado and New Mexico over the last 90 days is less than normal with the Sacramento Mountains now at less than 5 percent of normal (Figure 4b). Conservation storage in Elephant Butte Reservoir increased slightly from 4.4 percent full on October 25 to 5.0 percent on November 29, 2020 (Figure 4c).

The Rio Conchos basin in Mexico, which confluences into the Rio Grande just above Presidio and is an important source of water to the lower part of the Rio Grande in Texas, continues to show Severe drought with a dab of extreme conditions (Figure 4a). Combined conservation storage in Amistad and Falcon reservoirs increased over the past month from 46.8 percent on October 25 to 49.3 percent on November 29, about 20 percentage points below normal for this time of year (Figure 4d).

Figure 4a: The North American Drought Monitor for October 31, 2020 (source).

Figure 4b: Percent of normal precipitation for Colorado and New Mexico for the 90 days before November 29, 2020 (source). The red line is the Rio Grande Basin. I use this map to see check precipitation trends in the headwaters of the Rio Grande in southern Colorado, the main source of water to Elephant Butte Reservoir downstream.

Figure 4c: Reservoir storage in Elephant Butte Reservoir since 2018 with the median, min and max for measurements since 1990 (source).

Figure 4d: Reservoir storage in Amistad and Falcon reservoirs since 2018 with the median, min and max for measurements since 1990 (source).

A number of river/stream basins in the state have flows over the past seven days that are less than 25 percent of normal with about a dozen catchments with flows less than 10 percent of normal and five less than 5 percent of normal (Figure 5a). Statewide reservoir storage is at 79.8 percent full as of November 29, down from 80.3 percent a month ago, and about a percentage point below normal for this time of year (Figure 5b). Storage in individual reservoirs decreased from last month with some reservoirs falling back below 90 percent full (Figure 5c).

Figure 5a: Parts of the state with below-normal seven-day average streamflow as of November 29, 2020 (source).

Figure 5b: Statewide reservoir storage since 2018 compared to statistics (median, min and max) for statewide storage since 1990 (source).

Figure 5c: Reservoir storage as November 29, 2020 in the major reservoirs of the state (source).

Sea-surface temperatures in the Central Pacific entered La Niña conditions in August and have continued their cooling trend as projected (Figure 6a). The Climate Prediction Center increased the chance of La Niña conditions continuing through the winter (through March) from ~85 percent last month to ~95 percent this month with a ~65 percent chance of continuing through the spring (through May; Figure 6b).

Figure 6a. Forecasts of sea-surface temperature anomalies for the Niño 3.4 Region as of October 19, 2020 (modified from source).

Figure 6b. Probabilistic forecasts of El Niño, La Niña and La Nada conditions (source).

The U.S. Seasonal Drought Outlook through January 31, 2021 projects drought persistence and development in almost all of Texas (Figure 7a). The three-month temperature outlook projects warmer-than-normal conditions statewide with greater warming to the southwest (Figure 7b) while the three-month precipitation slightly favors drier-than-normal conditions for the state (Figure 7c).

Figure 7a: The U.S. Seasonal Drought Outlook for November 19, 2020, through February 2021 (source).

Figure 7b: Three-month temperature outlook from November 19, 2020 (source).

Figure 7c: Three-month precipitation outlook from November 19, 2020 (source).

Author

Robert Mace

Robert Mace

Executive Director & Chief Water Policy Officer at The Meadows Center for Water and the Environment

Robert Mace is the Executive Director and the Chief Water Policy Officer at the Meadows Center. He is also Professor of Practice in the Department of Geography at Texas State University. Robert has over 30 years of experience in hydrology, hydrogeology, stakeholder processes, and water policy, mostly in Texas.