Forecasters Predict a Slightly Above Average Hurricane Season for 2018

By Diane Cooper, Kingwood resident with 20+ years’ experience in weather and river forecasting for the National Weather Service

Colorado State University (CSU) released its initial 2018 Hurricane Outlook on April 5. It indicates an Above Normal Hurricane Season.

They predict:

  • 14 named storms
  • 7 hurricanes
  • 3 major hurricanes

The average number of tropical storms per year from 1981-2010:

  • 12 named storms
  • 6 hurricanes
  • 3 major hurricanes
Outlooks: Between Historical Averages and Near-Term Forecasts

Note: CSU outlooks are not near-term forecasts. Neither are they historical averages; that’s climate. Outlooks describe the probability of how any one season will likely vary from the average. To do that, scientists track numerous oscillations in the earth’s atmosphere and oceans. Historically, the high and low points of these oscillations have correlated highly with the presence or absence of hurricane formation. (For details about the Colorado State University Outlook, see their technical paper.

Key Factors Considered in This Hurricane Outlook

CSU indicates that Pacific and Atlantic Sea Surface Temperatures (SSTs) were key factors in formulating their early 2018 outlook.

The International Research Institute for Climate and Society and the NOAA Climate Prediction Center forecast the “ENSO phase.” (ENSO refers to El Niño/Southern Oscillation, which has three phases: El Niño, Neutral, and La Niña.)

Both groups predict that the current weak La Niña will transition to an ENSO-neutral phase during this spring or early summer. However, they do not anticipate a significant El Niño for this summer or fall. (Note: ENSO models tend to be more accurate from June to December than from February to May. So, a March outlook contains more uncertainty.) For more information about the ENSO forecasts, see the International Research Institute (IRI) ENSO Forecast.

Neutral Conditions in Pacific Favor Hurricane Development in Atlantic

El Niño conditions in the Pacific (above-average SSTs that are tracked over a 3-month period)  typically increase wind shear in the Caribbean and Atlantic. That reduces the chances of hurricanes fully organizing and strengthening, however we can still experience tropical systems and hurricanes with El Niño conditions.

Neutral ENSO conditions, on the other hand,  allow for normal wind shear patterns over the areas in the Atlantic Ocean where tropical development tends to occur.  Decreased wind shear provides a more favorable environment for Atlantic hurricane development.

Atlantic Sea Temps Now Vary, Causing Uncertainty

Currently, the western tropical Atlantic Ocean is very warm, while portions of the eastern tropical Atlantic and far North Atlantic are cool. Thus, forecasters have difficulty predicting how warm waters will become during the peak Atlantic hurricane season. Atlantic hurricane season is June 1 through November 30th, but the peak is mid-August through mid-October.

The main area where forecasters study Atlantic SSTs is called the Atlantic hurricane Main Development Region (MDR). The MDR includes the tropical North Atlantic Ocean and Caribbean Sea between 9.5°N and 21.5°N latitude.

For more information about factors influencing hurricane outlooks and ENSO states, see What Influences the Long-Range Weather Outlooks.

Difference Between Tropical Storms and Hurricanes

Sustained wind speeds determine the classification of a tropical system.

  • Tropical Depression – 38 mph or less
  • Tropical Storm  39 mph to 73 mph.
  • Hurricane – 74 mph and higher.
  • Major Hurricane  111 mph and higher. These are Category 3, 4 or 5 storms that have significant impacts, especially if the center of the storm comes ashore.

This video shows types of damage to expect as wind speeds increase.

Why Hurricane Outlooks Matter

Serious damage can occur in any storm. However, a slightly above normal outlook increases the odds that a tropical system will reach the U.S. coast. That’s simply because we expect to have more storms. More storms increase chances that one will come ashore near us.

Be Prepared, Not Sorry

Despite the outlook for an above normal season, the U.S. and Texas may see no direct hit from a tropical system. Outlooks say nothing about where topical systems will make landfall.

However, multiple storms could strike the Texas coast, as they did in 2008, when the CSU team predicted a “well above average” hurricane season. Texas took four direct hits between July 23 and September 8. The eye of Hurricane Ike passed right over Kingwood, knocking out power for approximately two weeks. Ike was one of the most destructive hurricanes ever to hit Texas and one of the deadliest. It caused $19.3 billion in damages and killed 84 people.

Typical Hurricane Ike wind damage in Kingwood, TX, in 2008. Ike moved quickly and caused more wind than water damage in Kingwood. The opposite was true near the coast where a 22-foot storm surge wiped out thousands of homes on the Bolivar Peninsula.

The Atlantic hurricane season starts June 1st, so start preparing now. In my next post, I’ll talk about how to prepare for a hurricane.

In the meantime, also remember that it does not take a tropical system to produce significant rainfall in southeast Texas. The 2015 Memorial Day flood and the 2016 Tax Day Floods are recent examples of 500+ year floods not connected to a tropical system. We should always be prepared for potential flooding in this area.

Posted April 10, 2018, 224 Days after Hurricane Harvey