Forecasting where a hurricane will go and how strong it will be starts with data. Hurricane specialists at NOAA study satellite imagery and computer models to make forecast decisions for advisories that go to emergency managers, media and the public for hurricanes, tropical storms and tropical depressions.
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.
The number of tropical cyclone advisories issued in 2017
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 of tropical storm and hurricane-force winds at specific locations. A potential storm surge flooding map and a prototype 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.
When it comes to hurricanes, most people think of wind. But water from storm surge at the coast and inland flooding claims the most lives.
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.
Flooding levels from the combined effect of storm surge and tides in the Florida Keys during Hurricane Irma
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 25 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.
Beginning this year, NOAA's National Weather Service will 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.
The crews of the NOAA and U.S. Air Force Reserve hurricane hunter fleet fly around and directly into the storm’s center, measuring weather data to determine the storm’s location, structure and intensity.
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.
Total number of missions flown by NOAA and USAF Hurricane Hunters in 2017
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 MacDill Air Force Base in Tampa, 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.
Large-scale conditions in the Atlantic and the Caribbean Sea will determine how active or inactive a hurricane season will be.
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 be 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.
It only takes one storm that affects you to make it a bad hurricane season. If you live along the coast or in nearby areas affected by inland flooding, it’s essential to have a personal hurricane plan. This can mean the difference between your being a hurricane victim and a hurricane survivor.
The time to put together that plan is well before a hurricane hits. Find out if you live in a hurricane storm surge evacuation zone. If you do, know where you would have to go.
If you don’t need to evacuate, have the supplies you need to not just get through the storm, but for the potentially lengthy and unpleasant aftermath. Have enough non-perishable food, water and medicine to last each person in your family a minimum of one week.
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 Homesoffsite link (FLASH®) is a NOAA partner and the country’s leading consumer advocate for strengthening homes and safeguarding families from natural and manmade disasters.