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Congressional Research Service
Informing the legislative debate since 1914
0
August 29, 2017
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 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 closer, approximately
280 miles from the coast, land-based radars begin to
provide the NHC with precipitation and wind-velocity data.
Additional ground-based measurements are provided by the
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 forecast computer
models. The principal purpose of hurricane forecast models
typically is to predict the hurricane track and intensity over
a period of three to five days. Essentially, the model uses
the observational data to understand the state of the
atmosphere and then uses mathematical equations to
produce forecasts. Not all hurricane forecast 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
Using the results from hurricane forecast models, 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), 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 request that NWS
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