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Congressional Research Service
Informing the legislative debate since 1914
0
Updated July 11, 2019
Forecasting Hurricanes: Role of the National Hurricane Center
The National Hurricane Center (NHC), part of the National
Weather Service (NWS) within the National Oceanic and
Atmospheric Administration (NOAA), is responsible for
forecasting tropical cyclones, including hurricanes in the
Atlantic Ocean and the eastern Pacific Ocean. The NHC
provides estimates of the path of a tropical cyclone (i.e.,
hurricane track), the intensity, and the size and structure of
the storm, as well as predictions of storm surge, rainfall,
and even associated tornadoes. Depending on the status of
the tropical cyclone, this information may be used to create
a hurricane watch or a hurricane warning and public
advisories, which are issued on an increasingly frequent
basis if a storm strengthens and approaches the U.S.
coastline.
How the Process Works
A hurricane forecast involves many components and uses a
broad array of resources and capabilities within NOAA and
the NWS, all of which must be coordinated and interpreted
by the NHC. The process begins with observations:
satellites, aircraft, ships, buoys, radar, and other sources
provide data used to create storm-track and intensity
predictions. Most Atlantic hurricanes, for example, begin to
form just west of the African continent over the ocean.
NOAA weather satellites primarily provide the remote-
sensing observations during the early stages of tropical
storm development in the eastern Atlantic. NOAA's
Geostationary Operational Environmental Satellites
(GOES) are stationed over the same location spanning
North America (two satellites make up the active GOES
constellation, often referred to as GOES East and GOES
West) and provide continuous data as the storms form and
intensify during their journey across the Atlantic from
Africa to North America.
Approaching the Coast
If an Atlantic hurricane is judged to pose a threat to the U.S.
coastline, NOAA hurricane aircraft and U.S. Air Force
aircraft (often referred to as Hurricane Hunters) fly directly
into the storm to collect real-time data from inside the
cyclone. Within the NHC, it is the responsibility of the
Chief, Aerial Reconnaissance Coordination, All Hurricanes
(CARCAH) unit, to coordinate all tropical cyclone
operation reconnaissance in accordance with the National
Hurricane Operations Plan. Data collected from the
Hurricane Hunters and other aircraft (e.g., the NASA
Global Hawk) are checked at CARCAH and provided to
NHC forecasters. If the storm gets within 280 miles of the
coast, land-based radars begin to provide the NHC with
precipitation and wind-velocity data. Additional ground-
based measurements are provided by NOAA's Automated
Surface Observation Systems instruments when the storm is
close to shore or makes landfall.
Analyzing the Data
The NHC gathers all the observational data collected as a
tropical cyclone approaches the U.S. coastline and uses the
data to generate a series of hurricane forecasts, which
consider the output from numerical weather prediction
models. Typically, the principal purpose of the numerical
weather prediction models is to predict the hurricane track
and intensity over a period of three to five days. The models
use the observational data to understand the state of the
atmosphere and then use mathematical equations to produce
forecasts. Not all numerical weather prediction models are
the same; they may differ in how they process information,
such as when observations are fed into the model, which
equations are used, how the solutions to the equations are
used to make forecasts, and other factors. These differences
explain why NHC hurricane forecasts may differ from those
of other countries or institutions that also produce hurricane
forecasts (e.g., the European Center for Medium-Range
Forecasts produces Atlantic hurricane forecasts, as do some
research institutions within the United States, such as the
National Center for Atmospheric Research).
Forecasts and Warnings
Different components within and outside the NHC
contribute to the hurricane forecast process. These include
the Tropical Analysis and Forecast Branch (TAFB), the
Hurricane Specialist Unit (HSU), and the Hurricane Liaison
Team (HLT). Of these, the HSU produces the final, official
public forecast products, issued every six hours after a
storm forms and more frequently if a hurricane watch or a
hurricane warning is issued. (A hurricane watch is an
announcement that hurricane conditions are possible within
a specified coastal area, usually issued 48 hours in advance
of the onset of tropical-storm-force winds. A hurricane
warning is issued when hurricane conditions-sustained
winds 74 miles per hour [mph] or greater-are expected
somewhere within the specified coastal area.) The HSU
also provides briefings on tropical storms to emergency
managers and the public and cooperates with
meteorological services in other countries (e.g., Mexico, as
well as Central American and Caribbean countries). The
TAFB supports the HSU by providing tropical cyclone
position and intensity estimates, conducting media
interviews, and assisting in tropical cyclone operations.
The HLT is sponsored through the Federal Emergency
Management Agency (FEMA) and is comprised of federal,
state, and local emergency managers, FEMA personnel, and
NWS forecasters and hydrologists. On or before the
beginning of hurricane season (for the Atlantic, June 1 to
November 30; for the Pacific, May 15 to November 30), the
NHC director requests that FEMA activate the HLT, which
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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