Colorado State University Archives

Researchers at highly respected Colorado State University (CSU) issued their hurricane season forecast for 2021 last week. Like the University of Miami, AccuWeather and others, they predicted an above-average season based on sea-surface temperatures, the presence of La Niña, and historical analogs. CSU used data and models going back 40 years. Factors considered also include: where sea surface temperatures are warmer/cooler, sea level pressures, vertical wind shear levels (the change in wind direction and speed with height in the atmosphere), accumulated tropical cyclone energy, and more.

CSU Forecast Compared to Others

Here’s how CSU’s hurricane season forecast looks compared to historical averages and other predictions.

Year(s)	Storms	Hurricanes	Major Hurricanes
1981-2010 (Old Average)	12	6	3
1991-2020 (New Average)	14	7	3
2020 Actual	30	13	6
2021 Predicted by AccuWeather	16 to 20	7 to 10	3 to 5
2021 Predicted by Colorado State	17	8	4

Major Hurricanes are Cat 3 or higher with sustained winds of 111 mph or greater.

Striking Recent Parallels

According to CSU, so far, the 2021 hurricane season is exhibiting characteristics similar to 1996, 2001, 2008, 2011 and 2017. “All of our analog seasons had above-average Atlantic hurricane activity, with 1996 and 2017 being extremely active seasons,” said Phil Klotzbach, research scientist in the Department of Atmospheric Science and lead author of the CSU report.

In case you’re new to the Houston area and the significance of those bold-faced years escapes you:

2001 was Tropical Storm Allison which dumped 38 inches of rain on Houston, so much that it caused flood maps to be redrawn. The storm meandered over Houston for 4 days due to slow movement and weak steering currents.
2008 was Hurricane Ike which destroyed tens of thousands of homes on the Bolivar Peninsula. It killed 195 people, came ashore as a Cat 4 storm with winds of 148 miles per hour, came straight up Galveston Bay, went right over Kingwood, and knocked down so many trees that the Lake Houston Area lost power for 3 weeks. It did $38 billion in damage and ranks as the sixth costliest storm in US history.
2017 was Hurricane Harvey. HCFCD’s report on the storm says it all. At the peak of Harvey, five times more water went over the Lake Houston Dam than goes over Niagra Falls on average.

*Bolivar Peninsula after Hurricane Ike in 2008. Photo Courtesy of NOAA.*

*In 2019, NASA captured Dorian and this string of tropical cyclones lined up across the Western Hemisphere.*

But 2011 was the opposite end of the spectrum. It was the driest year ever for Texas and the start of a drought that lasted through 2014.

Playing the Percentages

The CSU team predicts that 2021 hurricane season activity will be about 140 percent of the average season. By comparison, 2020 was about 170 percent. The 2020 hurricane season had six landfalling continental US hurricanes, including Category 4 Hurricane Laura which battered southwestern Louisiana.

The report also includes the probability of major hurricanes making landfall:

69% for the entire U.S. coastline (average for the last century is 52%)
45% for the U.S. East Coast including the Florida peninsula (average for the last century is 31%)
44% for the Gulf Coast from the Florida panhandle westward to Brownsville (average for the last century is 30%)
58% for the Caribbean (average for the last century is 42%)

Keep your fingers crossed and make sure you’re prepared. It only takes one storm to make your life miserable if you are not prepared. And remember, Allison happened on June 4th…just three days after the start of hurricane season.

Posted by Bob Rehak on 4/10/2021 based on a report by Colorado State University

1320 Days since Hurricane Harvey

USA Today has reported that hurricane experts from Colorado State University (CSU) have predicted an above-average hurricane season this year. How much above average? About 140%, they say. In addition, CSU predicts a 69% chance for a MAJOR hurricane (Cat 3, 4 or 5) to strike the mainland U.S.

Warm Atlantic and El Niño Seen as Main Factors

Reasons: unusually warm seawater in the Atlantic and the likely LACK of an El Niño in the Pacific. El Niño in the Pacific usually sets up wind shear that tears apart storms in the Atlantic. Said another way, they help keep tropical storms from developing into full-force hurricanes. But without El Niño, the lack of shear allows more storms to develop and creates active hurricane seasons.

*Source: NOAA, From April 2, 2020. Shows most of Atlantic has above-normal sea-surface temps, and that temps immediately offshore the upper Texas and Louisiana Coasts are now 4-5 degrees above normal.*

CSU predicts 18 named storms will develop.

AccuWeather released its hurricane season predictions a week earlier. They predict 14-18 names storms. Of those, seven to nine will likely become hurricanes, and two to four are likely to hit the U.S. mainland.

NOAA should issue its forecast in late May.

Hurricane season extends from June 1 to November 30.

March Warmth Unrelated to Hurricane Season

Jeff Lindner, Harris County Flood Control’s meteorologist, says that the unusually warm March that south Texas just experienced (about 8 degrees above normal) will have little effect on tropical storm formation. “There is some correlation with a warm Gulf of Mexico and severe weather and flooding along the Gulf Coast during the spring months. But there is little to no correlation to tropical activity in the Gulf during summer months.”

3-4 Inches of Rain Possible in Next 5 Days

Speaking of Spring rains, Lindner also predicts a stormy weather pattern will set up over our area for the next 5-7 days. He says “some severe weather and heavy rainfall will be possible.”

“Widespread rainfall amounts of 1-2 inches with isolated totals of 3-4 inches will be possible between this afternoon and Saturday,” says Lindner. He predicts the heaviest rainfall across area north of I-10. Storms could train, producing the higher rainfall amounts. But Lindner also adds, “It has been dry of late and the soil can take several inches of rainfall as long as it is not all at once.” So no one is talking about flooding at this point.

NOAA predicts a slight chance of severe storms Friday evening, mostly west of Houston.

Here’s where NOAA predicts the heaviest rains to fall during the next 5 days and what the total accumulations should be.

Posted by Bob Rehak on 4/2/2020

947 Days since Hurricane Harvey

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Colorado State Experts Predict Another Hurricane Season Like 2001, 2008 and 2017