Hurricane forecasting

Key data come from NOAA satellites that orbit the earth, continuously observing tropical cyclones (hurricane, tropical storm or tropical depression) from start to finish. Polar-orbiting satellites fly over the storm about twice a day at a lower altitude, carrying microwave instruments that reveal storm structure. If there’s a chance the cyclone will threaten land, NOAA’s National Hurricane Center (NHC) sends U.S. Air Force Reserve and NOAA hurricane hunter aircraft to fly through a storm to take detailed observations. NHC hurricane specialists also analyze a variety of computer models to help forecast a tropical cyclone. Each storm is different, and no one model is right every time, so the specialists’ experience with these different models is crucial to making the best forecast. 

When a tropical cyclone threatens the U.S. coast, NHC confers with meteorologists at NOAA’s National Weather Service forecast offices in the path of the storm to coordinate any necessary watches and warnings in those communities.

Every six hours NHC will issue updated text and graphics — all available on hurricanes.gov — that include track and intensity forecast for the next five days, along with the chances and time of arrival of tropical storm and hurricane-force winds at specific locations. A potential storm surge flooding map and storm surge watch/warning graphic are included. NHC also posts the same information on social media to ensure a wide distribution.

When watches or warnings are posted for the U.S. coastline, NHC opens a television media pool to give live interviews to national news outlets and the local TV stations in the path of the storm.

Hurricane winds are rated from 1 to 5 on the Saffir-Simpson Hurricane Wind Scale. Based on maximum sustained winds, the scale gives examples of types of potential property damage and impacts.

Yet, nearly half of the lives lost in a hurricane are related to storm surge, an abnormal rise of water over and above the predicted astronomical tides. Storm surge can be particularly severe if it coincides with normal high tide, resulting in storm tides reaching up to 20 feet or more in some cases. 

And 27 percent of hurricane fatalities are due to inland flooding. Heavy rainfall can extend for hundreds of miles inland, producing extensive inland flooding as creeks and rivers overflow.

And it isn’t just hurricanes that carry the most water — some of the worst flooding on record has been caused by tropical storms.

To better prepare communities for storm surge, NOAA’s National Hurricane Center has developed a potential storm surge flooding map, which is released when there is a hurricane watch or warning along the U.S. East or Gulf Coast.  The map shows where storm surge flooding could occur in a near worst case scenario and gives the height in three feet intervals that water could reach above normal dry ground.

In 2017, NOAA's National Weather Service began to issue Storm Surge Watches and Warnings to highlight areas along the Gulf and Atlantic coasts of the continental United States that have a significant risk of life-threatening inundation from a tropical, subtropical, post-tropical, or potential tropical cyclone.

NHC will begin providing an experimental graphic in 2020 that will depict the expected storm surge inundation values for the United States Gulf and Atlantic coasts, Puerto Rico, and the U.S. Virgin Islands that are provided in the tropical cyclone public advisory (TCP).  These values represent the peak height the water could reach above normally dry ground somewhere within the specified areas.

When hurricane specialists at NOAA’s National Hurricane Center need a closer look at a developing storm or major hurricane, they send special “hurricane hunter” aircraft to fly into it.

Most of the hurricane hunters are the ten WC-130J aircraft of the Air Force Reserve 53rd Weather Reconnaissance Squadron at Keesler Air Force Base in Biloxi, Mississippi. NOAA’s two WP-3 Orion aircraft from Lakeland Regional Airport in Lakeland, Florida, are used mostly for research to improve hurricane forecasts.

Flying directly into the storm’s center, these turbo propeller planes drop probes called dropwindsondes from a chute in the aircraft’s belly at strategic points. Dropwindsondes continuously transmit critical weather data back to the plane, including pressure, humidity, temperature, wind direction and wind speed. The data give a detailed picture of the storm’s structure and intensity. The planes also have a special microwave radiometer that measures surface wind and the rate of rain.

All this data is then relayed from the plane to a satellite and then to NHC where hurricane specialists put it together to assess the cyclone’s strength, motion, and size. Radar data from NOAA and USAF hurricane hunters are fed into computer models to help forecasters make as accurate a forecast as possible, and to help hurricane researchers achieve a better understanding of storm processes.

It’s not always a bumpy ride. NOAA also has a G-IV jet that cruises 45,000 feet above and around a storm. It can cover thousands of square miles around a storm, using dropwindsondes and Doppler radar to collect different type of data from the storm’s core and surrounding environment. The data is sent to NOAA’s National Centers for Environmental Prediction in College Park, Maryland, where it’s used in computer models that have been able to improve hurricane track forecasts by about 20 percent in recent years. 

The number of storms in an Atlantic hurricane season depends on the large-scale atmospheric and oceanic environment in the areas where storms develop, in the tropical North Atlantic Ocean and the Caribbean Sea. Global phenomenon such as El Niño triggered by ocean warming in the equatorial Pacific may also affect whether Atlantic hurricanes develop.

Scientists say that while the historical record shows an increase in the numbers of Atlantic hurricanes since the early 1900s, this record does not reflect how much easier it has become to identify hurricanes since we began using satellites. Once this is factored in, scientists say there has been no significant overall increase in Atlantic hurricanes since the late 1800s.

On a shorter timeframe, however, the numbers of Atlantic hurricanes have increased, much of it beginning in 1995, as the tropical North Atlantic warmed and atmospheric conditions became conducive to increased hurricane activity, similar to what occurred during the mid-20th century.

One influence is a variation in North Atlantic Ocean temperatures called the Atlantic Multi-decadal Oscillation (AMO), that has cool and warm phases historically lasting 25-40 years each. During its warm phase, North Atlantic sea-surface temperatures are unusually warm compared to the tropical average and the atmospheric conditions over the Atlantic are conducive to hurricane activity. The recent multidecadal variations in Atlantic sea surface temperatures may be partly due to human-caused factors such as dust or other aerosols and partly due to natural climate variability.  Scientists are continuing to work to better understand the relative contributions of these factors to the recent multidecadal variability.

Human-caused increases in greenhouse gases have very likely contributed to the warming of tropical North Atlantic sea-surface temperatures observed over the past century. The World Meteorological Organization in 2010 concluded that by the late 21st century greenhouse warming is not expected to increase the number of tropical cyclones, but is expected to increase the average intensity of tropical cyclones. Near-storm rainfall rates are also expected to increase. 

Remember, for a hurricane, we evacuate in the U.S. due to the impacts of water, not wind. So if you do not live in an evacuation zone and your home is structurally sound, you should shelter-in-place. Have the supplies you need to get through the storm and for the potentially lengthy and unpleasant aftermath, with enough non-perishable food, water and medicine to last each person in your family a minimum of one week.

But if you do live in an evacuation zone, things are different in 2020 due to the COVID-19 pandemic. The shelter location may be different, so find out now what's available to you. If you need to evacuate, have a “go kit” with personal items you cannot do without during an emergency. This will include items that can help protect you and others from COVID-19, such as hand sanitizer or, if that's not available, bar or liquid soap, and at least two cloth face coverings for each person who is two years old and older.

Today you can determine your personal hurricane risk, find out if you live in a hurricane evacuation zone, and review/update insurance policies. You can also make a list of items to replenish hurricane emergency supplies and start thinking about how you will prepare your home for the coming hurricane season. If you live in hurricane-prone areas, you are encouraged to complete these simple preparations before hurricane season begins on June 1.  Keep in mind, you may need to adjust any preparedness actions based on the latest health and safety guidelines from the CDC and your local officials. 

Waiting until the storm is on your doorstep is too late. Resilience depends on preparation. The websites www.hurricanes.gov/prepare and www.ready.gov will help you make a plan for yourself and your loved ones.

NOAA’s Weather-Ready Nation campaign is about building community resilience in the face of increasing vulnerability to extreme weather and water event, including hurricanes.

The nonprofit Federal Alliance for Safe Homes offsite link (FLASH®) is a NOAA partner and the country’s leading consumer advocate for strengthening homes and safeguarding families from natural and manmade disasters.