Updated July 11, 2019
Forecasting Hurricanes: Role of the National Hurricane Center
The National Hurricane Center (NHC), part of the National
Analyzing the Data
Weather Service (NWS) within the National Oceanic and
The NHC gathers all the observational data collected as a
Atmospheric Administration (NOAA), is responsible for
tropical cyclone approaches the U.S. coastline and uses the
forecasting tropical cyclones, including hurricanes in the
data to generate a series of hurricane forecasts, which
Atlantic Ocean and the eastern Pacific Ocean. The NHC
consider the output from numerical weather prediction
provides estimates of the path of a tropical cyclone (i.e.,
models. Typically, the principal purpose of the numerical
hurricane track), the intensity, and the size and structure of
weather prediction models is to predict the hurricane track
the storm, as well as predictions of storm surge, rainfall,
and intensity over a period of three to five days. The models
and even associated tornadoes. Depending on the status of
use the observational data to understand the state of the
the tropical cyclone, this information may be used to create
atmosphere and then use mathematical equations to produce
a hurricane watch or a hurricane warning and public
forecasts. Not all numerical weather prediction models are
advisories, which are issued on an increasingly frequent
the same; they may differ in how they process information,
basis if a storm strengthens and approaches the U.S.
such as when observations are fed into the model, which
coastline.
equations are used, how the solutions to the equations are
used to make forecasts, and other factors. These differences
How the Process Works
explain why NHC hurricane forecasts may differ from those
A hurricane forecast involves many components and uses a
of other countries or institutions that also produce hurricane
broad array of resources and capabilities within NOAA and
forecasts (e.g., the European Center for Medium-Range
the NWS, all of which must be coordinated and interpreted
Forecasts produces Atlantic hurricane forecasts, as do some
by the NHC. The process begins with observations:
research institutions within the United States, such as the
satellites, aircraft, ships, buoys, radar, and other sources
National Center for Atmospheric Research).
provide data used to create storm-track and intensity
predictions. Most Atlantic hurricanes, for example, begin to
Forecasts and Warnings
form just west of the African continent over the ocean.
Different components within and outside the NHC
NOAA weather satellites primarily provide the remote-
contribute to the hurricane forecast process. These include
sensing observations during the early stages of tropical
the Tropical Analysis and Forecast Branch (TAFB), the
storm development in the eastern Atlantic. NOAA’s
Hurricane Specialist Unit (HSU), and the Hurricane Liaison
Geostationary Operational Environmental Satellites
Team (HLT). Of these, the HSU produces the final, official
(GOES) are stationed over the same location spanning
public forecast products, issued every six hours after a
North America (two satellites make up the active GOES
storm forms and more frequently if a hurricane watch or a
constellation, often referred to as GOES East and GOES
hurricane warning is issued. (A hurricane watch is an
West) and provide continuous data as the storms form and
announcement that hurricane conditions are possible within
intensify during their journey across the Atlantic from
a specified coastal area, usually issued 48 hours in advance
Africa to North America.
of the onset of tropical-storm-force winds. A hurricane
warning is issued when hurricane conditions—sustained
Approaching the Coast
winds 74 miles per hour [mph] or greater—are expected
If an Atlantic hurricane is judged to pose a threat to the U.S.
somewhere within the specified coastal area.) The HSU
coastline, NOAA hurricane aircraft and U.S. Air Force
also provides briefings on tropical storms to emergency
aircraft (often referred to as Hurricane Hunters) fly directly
managers and the public and cooperates with
into the storm to collect real-time data from inside the
meteorological services in other countries (e.g., Mexico, as
cyclone. Within the NHC, it is the responsibility of the
well as Central American and Caribbean countries). The
Chief, Aerial Reconnaissance Coordination, All Hurricanes
TAFB supports the HSU by providing tropical cyclone
(CARCAH) unit, to coordinate all tropical cyclone
position and intensity estimates, conducting media
operation reconnaissance in accordance with the National
interviews, and assisting in tropical cyclone operations.
Hurricane Operations Plan. Data collected from the
Hurricane Hunters and other aircraft (e.g., the NASA
The HLT is sponsored through the Federal Emergency
Global Hawk) are checked at CARCAH and provided to
Management Agency (FEMA) and is comprised of federal,
NHC forecasters. If the storm gets within 280 miles of the
state, and local emergency managers, FEMA personnel, and
coast, land-based radars begin to provide the NHC with
NWS forecasters and hydrologists. On or before the
precipitation and wind-velocity data. Additional ground-
beginning of hurricane season (for the Atlantic, June 1 to
based measurements are provided by NOAA’s Automated
November 30; for the Pacific, May 15 to November 30), the
Surface Observation Systems instruments when the storm is
NHC director requests that FEMA activate the HLT, which
close to shore or makes landfall.
remains active throughout hurricane season. If a tropical
cyclone in the Atlantic or eastern Pacific basin threatens
either the United States or its territories, then the NHC can
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Forecasting Hurricanes: Role of the National Hurricane Center
request that NWS meteorologists or hydrologists be
predicting landfall location. That increased accuracy
assigned to the HLT until the storm threat has passed.
provides useful information to local, state, and federal
emergency managers faced with decisions about evacuating
The HLT serves as a liaison between the NHC forecasters
coastlines and staging emergency equipment and supplies.
and local emergency managers facing a threat of tropical
Better instruments aboard weather satellites, such as the
cyclones. A main function of the HLT is to communicate
GOES series and the polar-orbiting weather satellites, have
the level of the threat to federal, state, and local officials.
contributed to those improvements, together with more
Neither the HLT nor the NHC assumes any responsibility
sophisticated hurricane forecast models and vastly
for issuing evacuations, however; those decisions are left to
improved computing capabilities.
state or local officials.
Flooding resulting from intense precipitation during
Forecasts and warnings generally are coordinated between
hurricanes could be responsible for the majority of fatalities
the NWS national centers and the local forecast offices.
caused by a storm. Some studies show, however, that the
When the NHC issues its forecast, local NWS Weather
amount of rainfall produced by a storm may not necessarily
Forecast Offices use the information for their own
be related to the intensity of the hurricane. Intense
forecasts, which take into consideration local conditions.
precipitation and flooding during Hurricane Harvey, for
example, continued even after the storm made landfall and
Storm Surge
was downgraded from a hurricane to a tropical storm.
In addition to the hurricane forecast models that predict
Improving the ability to accurately forecast the amount and
intensity, winds, and precipitation, other forecast models
location of intense precipitation would advance the value of
are designed specifically to forecast storm surge. Storm
hurricane forecasting significantly.
surge is defined as an abnormal rise in sea level
accompanying a hurricane or other intense storm. It
Perhaps the biggest challenge for the NHC is how to
generally refers to the difference between the measured
improve the ability to predict hurricane intensity, basically
level of the sea surface during the storm compared to what
how strong a hurricane will become and when and where it
the sea level would have been without a storm. (See Figure
will reach its maximum intensity. Hurricane intensity is
1.) Storm surge, especially when combined with high
generally measured as highest sustained wind speeds,
precipitation from a hurricane, can create dangerous flood
referred to as the Saffir-Simpson wind scale (1-5), ranging
conditions for coastal communities during tropical cyclones
from sustained winds of 74-95 mph (Category 1) to 157
and other intense storms. (Superstorm Sandy, for example,
mph or higher (Category 5). However, that measurement
produced a storm surge that inundated the heavily
does not take into consideration the storm surge or
populated coastline in New Jersey and New York to cause
precipitation-caused flooding, both of which may be among
enormous damage, despite the storm itself being a relatively
the most dangerous elements of a hurricane. (For instance,
weak hurricane immediately prior to landfall.)
intense, concentrated, and multiday precipitation and
flooding in and around the Houston, TX, region caused by
Figure 1. Storm Surge
Hurricane Harvey has been the storm’s most destructive
and dangerous feature.) Despite not being part of the
hurricane-intensity scale, hurricane forecast information
typically includes precipitation estimates—as in the case of
Hurricane Harvey—and storm-surge estimates, so that
affected communities may better prepare for the impending
hazard.
Legislation
The 115th Congress enacted P.L. 115-25, the Weather
Research and Forecasting Act of 2017, which provides
direction to NOAA and NWS on a broad range of weather-
Source: National Hurricane Center at http://www.nhc.noaa.gov/
related activities. The primary aim of the legislation is to
surge/ssu.php.
improve NOAA’s weather forecasts and warnings. Section
104 of Title 1 of P.L. 115-25 is specifically aimed at
The Storm Surge Unit, part of the NHC, models and
improving hurricane forecasting. For more detailed
predicts storm-surge vulnerability over the U.S. Atlantic
information about P.L. 115-25, see CRS Report R44838,
and Gulf coasts, Hawaii, Puerto Rico, and the U.S. Virgin
The Weather Research and Forecasting Innovation Act of
Islands. The Storm Surge Unit typically commences its
2017: Congressional Direction to NOAA in P.L. 115-25, by
operations when a hurricane warning is issued and
Peter Folger.
continues 24 hours per day if the hurricane threatens to
make landfall until the storm surge threat subsides.
Eva Lipiec, Analyst in Natural Resources Policy
Challenges
Peter Folger,
Specialist in Energy and Natural
Hurricane forecasts have improved in recent decades. In
Resources Policy
1992, hurricane forecasts extended out only three days;
IF10719
today, the forecasts typically extend for five days. Over that
same time span, the ability to forecast hurricane tracks also
has improved, increasing the likelihood of more accurately
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Forecasting Hurricanes: Role of the National Hurricane Center


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