NHC Graphical Product Descriptions
Download the NHC Product Description User's Guide for all tropical cyclone-related products.
Contents
Tropical Cyclone Track Forecast Cone and Watches/Warnings
This graphic shows an approximate representation of coastal areas under a hurricane warning (red), hurricane watch (pink), tropical storm warning (blue) and tropical storm watch (yellow). The orange circle indicates the current position of the center of the tropical cyclone. The black line and dots show the National Hurricane Center (NHC) forecast track of the center at the times indicated. The dot indicating the forecast center location will be black if the cyclone is forecast to be tropical and will be white with a black outline if the cyclone is forecast to be extratropical. If only an L is displayed, then the system is forecast to be a remnant low. The letter inside the dot indicates the NHC's forecast intensity for that time:
D: Tropical Depression – wind speed less than 39 MPH
S: Tropical Storm – wind speed between 39 MPH and 73 MPH
H: Hurricane – wind speed between 74 MPH and 110 MPH
M: Major Hurricane – wind speed greater than 110 MPH
NHC tropical cyclone forecast tracks can be in error. This forecast
uncertainty is conveyed by the track forecast "cone", the solid white
and stippled white areas in the graphic. The solid white area depicts
the track forecast uncertainty for days 1-3 of the forecast, while the
stippled area depicts the uncertainty on days 4-5. Historical data
indicate that the entire 5-day path of the center of the tropical
cyclone will remain within the cone about 60-70% of the time. To
form the cone, a set of imaginary circles are placed along the
forecast track at the 12, 24, 36, 48, 72, 96, and 120 h positions,
where the size of each circle is set so that it encloses 67% of the
previous five years official forecast errors. The cone is then formed
by smoothly connecting the area swept out by the set of circles.
There is also uncertainty in the NHC intensity forecasts. The Maximum
1-minute Wind Speed Probability Table described below provides
intensity forecast and uncertainty information.
It is also important to realize that a tropical cyclone is not a point. Their
effects can span many hundreds of miles from the center. The area
experiencing hurricane force (one-minute average wind speeds of at least
74 mph) and tropical storm force (one-minute average wind speeds of
39-73 mph) winds can extend well beyond the white areas shown enclosing
the most likely track area of the center. The distribution of hurricane
and tropical storm force winds in this tropical cyclone can be seen in
the Cumulative Wind History Graphic described below.
Considering the combined forecast uncertainties in track, intensity, and size, the
chances that any particular location will experience winds of 34 kt (tropical storm force),
50 kt, or 64 kt (hurricane force) from this tropical cyclone are presented in
graphical form and in
tabular form for selected locations and forecast positions.
Graphics for Atlantic tropical cyclones are normally issued every six hours at
5:00 AM EDT, 11:00 AM EDT, 5:00 PM EDT, and 11:00 PM EDT (or 4:00 AM EST, 10:00 AM EST, 4:00 PM EST, and 10:00 PM EST).
Graphics for Eastern Pacific tropical cyclones are normally issued every six hours at
2:00 AM PDT, 8:00 AM PDT, 2:00 PM PDT, and 8:00 PM PDT (or 1:00 AM PST, 7:00 AM PST, 1:00 PM PST, and 7:00 PM PST).
The graphics also will be updated when intermediate public advisories are issued, and special graphics may be issued at
any time due to significant changes in warnings or in the cyclone.
Note: A detailed definition of the NHC track forecast cone is also available.
Tropical Cyclone Surface Wind Speed Probabilities
Three types of tropical cyclone wind speed probability values are created for each forecast/advisory package, but not all
of these values are distributed or placed on the Internet. For each probability value, the event in question is a
sustained (one-minute average) surface (10 m) wind speed of at least a particular threshold value (34 kt...39 mph, 50 kt...58 mph, or 64 kt...74 mph)
at a specific location.
Cumulative – These values tell you the overall probability the event will
occur sometime during the specified cumulative forecast period (0-6 hours, 0-12,
0-18, etc.) at each specific point. These values are provided in both the text and
graphical formats.
In the text product, the numbers are in parentheses.
The graphical products depict
only cumulative values. The text product is transmitted
to users via normal NWS dissemination methods. The graphic is available on the internet from the
National Hurricane Center and the
Central Pacific Hurricane Center.
Individual – These values tell you the probability the event will start
sometime during the specified individual forecast period (0 - 6 hours, 6-12, 12-18,
etc.) at each specific point. These periods are individual, since nothing that
occurs before or after the specified period affects the probability. These values
are provided only in the text NHC product. They are the values outside of the
parentheses (cumulative values are in the parentheses). The term "individual" also
makes a clear distinction from the cumulative period values for users.
Graphics for Atlantic tropical cyclones are normally issued every six hours at
5:00 AM EDT, 11:00 AM EDT, 5:00 PM EDT, and 11:00 PM EDT (or 4:00 AM EST, 10:00 AM EST, 4:00 PM EST, and 10:00 PM EST).
Graphics for Eastern Pacific tropical cyclones are normally issued every six hours at
2:00 AM PDT, 8:00 AM PDT, 2:00 PM PDT, and 8:00 PM PDT (or 1:00 AM PST, 7:00 AM PST, 1:00 PM PST, and 7:00 PM PST).
Special graphics may be issued at any time due to significant changes in warnings or in the cyclone.
Note: A more detailed description of these probability products is also available.
Tropical Cylone Surface Wind Field
This graphic shows the areas potentially being affected by the sustained winds of tropical storm
force (in orange) and hurricane force (in red). The display is based on the wind radii contained in the latest Forecast/Advisory
(indicated at the top of the figure). Users are reminded that the Forecast/Advisory wind radii represent the
maximum possible extent of a given wind speed within particular quadrants around the tropical cyclone. As a result,
not all locations falling within the orange or red shaded areas will be experiencing sustained tropical storm or
hurricane force winds, respectively.
In addition to the wind field, this graphic shows an approximate representation of coastal areas under a hurricane
warning (red), hurricane watch (pink), tropical storm warning (blue) and tropical storm watch (yellow). The white
dot indicates the current position of the center of the tropical cyclone, and the dashed line shows the history of
the center of the tropical cyclone.
Graphics for Atlantic tropical cyclones are normally issued every six hours at 5:00 AM EDT, 11:00 AM EDT, 5:00 PM
EDT, and 11:00 PM EDT (or 4:00 AM EST, 10:00 AM EST, 4:00 PM EST, and 10:00 PM EST). Graphics for Eastern Pacific
tropical cyclones are normally issued every six hours at 2:00 AM PDT, 8:00 AM PDT, 2:00 PM PDT, and 8:00 PM PDT
(or 1:00 AM PST, 7:00 AM PST, 1:00 PM PST, and 7:00 PM PST).
Special graphics may be issued at any time due to significant changes in warnings or in the cyclone.
Note: Please read the Tropical Cyclone Surface Wind Field full product description.
Cumulative Wind History
This graphic shows how the size of the storm has changed, and the areas
potentially affected so far by sustained winds of tropical storm force (in
orange) and hurricane force (in red). The display is based on the wind
radii contained in the set of Forecast/Advisories indicated at the top of
the figure. Users are reminded that the Forecast/Advisory wind radii
represent the maximum possible extent of a given wind speed within
particular quadrants around the tropical cyclone. As a result, not all
locations falling within the orange or red swaths will have experienced
sustained tropical storm or hurricane force winds, respectively.
Graphics for Atlantic tropical cyclones are normally issued every six hours at
5:00 AM EDT, 11:00 AM EDT, 5:00 PM EDT, and 11:00 PM EDT (or 4:00 AM EST, 10:00 AM EST, 4:00 PM EST, and 10:00 PM EST).
Graphics for Eastern Pacific tropical cyclones are normally issued every six hours at
2:00 AM PDT, 8:00 AM PDT, 2:00 PM PDT, and 8:00 PM PDT (or 1:00 AM PST, 7:00 AM PST, 1:00 PM PST, and 7:00 PM PST).
Special graphics may be issued at any time due to significant changes in warnings or in the cyclone.
Maximum 1-minute Wind Speed Probability Table
The table shows the probability that the maximum sustained (1-minute) surface (10 meter elevation) wind
speed of the tropical cyclone will be within various intensity ranges (dissipated, tropical depression,
tropical storm and hurricane) and for the five categories on the Saffir-Simpson Hurricane Scale during
the next 120 hours. These probabilities apply to the maximum sustained surface wind associated with the
cyclone, and not to winds that could occur at specific locations.
The probabilities are based on forecast errors during recent years in the official track and intensity
forecasts issued by the TPC/NHC. The probabilities are computed from the same method that creates the
individual location specific wind speed probabilities.
Graphics for Atlantic tropical cyclones are normally issued every six hours at 5:00 AM EDT, 11:00 AM EDT,
5:00 PM EDT, and 11:00 PM EDT (or 4:00 AM EST, 10:00 AM EST, 4:00 PM EST, and 10:00 PM EST).
Graphics for Eastern Pacific tropical cyclones are normally issued every six hours at 2:00 AM PDT,
8:00 AM PDT, 2:00 PM PDT, and 8:00 PM PDT (or 1:00 AM PST, 7:00 AM PST, 1:00 PM PST, and 7:00 PM PST).
Special graphics may be issued at any time due to significant changes in warnings or in the cyclone.
Graphical Tropical Weather Outlook
Example Graphical Tropical Weather Outlook for the Atlantic basin. (Click for another example with mouseovers)
The graphical Tropical Weather Outlook (TWO) is a web display that the National Hurricane Center (NHC) began testing
during the 2007 hurricane season. The Graphical TWO is intended to be a visual companion product to the text TWO. The
NHC produces a graphical TWO four times daily in both the Atlantic and Pacific basins.
The graphical TWO is usually available shortly after the text TWO has been issued, but occasionaly there might be a slight
delay for the updated graphic to appear on the NHC website. For this reason, users are reminded that the text TWO may show
updated information a few minutes prior to the graphical TWO.
For the Atlantic basin, the Graphical TWO is issued from June 1 to November 30 at 2:00 AM, 8:00 AM, 2:00 PM, and 8:00
PM EDT. For the Eastern Pacific basin, the Graphical TWO is issued from May 15 to November 30 at 5:00 AM, 11:00 AM,
5:00 PM, and 11:00 PM PDT. During Standard Time, the graphic is issued one hour earlier than the times indicated above.
A special TWO may be issued at any time when important changes in areas of disturbed weather over tropical or subtropical
waters need to be conveyed before the next scheduled release of the TWO.
Note: A more complete description of the Graphical Tropical Weather Outlook can be found here.
Tropical Cyclone Storm Surge Probabilities (2 - 25 feet)
The Tropical Cyclone Storm Surge Probabilities product consists of a graphic and GRIB2 data for creating the graphic for the Gulf
of Mexico and Atlantic coastal areas of the continental United States. This product is intended to provide users with information which enhances their ability to make preparedness
decisions specific to their own situations.
The graphic shows probabilities, in percent, of storm surge
exceeding various thresholds. In 2009, the range of thresholds were expanded and include data at 1-foot intervals. A minimum value of 2
feet and a maximum value of 25 feet will be available.
This storm surge graphic is based upon an ensemble of Sea, Lake, and Overland Surge from Hurricanes (SLOSH)
model runs using the National Hurricane Center (NHC) official advisory and accounts for track, size, and intensity errors based
on historical errors. Additional information on the SLOSH model can be found at:
http://www.nhc.noaa.gov/ssurge/ssurge_slosh.shtml.
The emergency management community is the primary target audience. However, this product will also be widely used by other
federal, state, and local government agencies; the media; maritime interests; and the general public.
The product is available on the NHC website whenever a hurricane watch or hurricane warning is in effect for any portion of the Gulf or Atlantic
coasts of the continental United States. Updates to the product are produced about one hour after the issuance of routine
NHC tropical cyclone advisories at 5:00 AM EDT, 11:00 AM EDT, 5:00 PM EDT, and 11:00 PM EDT (or 4:00 AM EST, 10:00 AM EST, 4:00 PM EST,
and 10:00 PM EST).
Note: Read a more complete description of the Storm Surge Probabilities (2 - 25 feet).
Tropical Cyclone Storm Surge Probabilities (exceedance)
The Probabilistic Tropical Cyclone Storm Surge Exceedance products consist
of a graphic and
GRIB2 data for
creating the graphic for the Gulf of Mexico
and Atlantic coastal areas. The exceedance products show storm surge height
in feet, above normal tide levels, such that there is an N percent chance of
exceeding it, where N ranges from 10 to 90 in intervals of 10 percent. The
10 percent exceedance height, for example, is the storm surge height, above
normal tide levels, such that there is a 10 percent chance of exceeding it.
The storm surge graphics are based upon an ensemble of Sea, Lake, and
Overland Surge from Hurricanes (SLOSH) model runs using the National
Hurricane Center (NHC) official advisory and account for track, size, and
intensity uncertainty from historical errors. Additional information on the
SLOSH model can be found at:
http://www.nhc.noaa.gov/ssurge/ssurge_slosh.shtml.
The emergency management community is the primary target audience. However,
this product will also be widely used by other federal, state, and local
government agencies; the media; maritime interests; and the general public.
The product is available on the
NWS Meteorological Data Laboratory (MDL)
website whenever a hurricane watch or hurricane warning is in effect for any
portion of the Gulf or Atlantic coasts of the continental United States.
Updates to the product are produced about one hour after the issuance of
routine NHC tropical cyclone advisories at 5:00 AM EDT, 11:00 AM EDT, 5:00
PM EDT, and 11:00 PM EDT (or 4:00 AM EST, 10:00 AM EST, 4:00 PM EST, and
10:00 PM EST).
Note: You may also read the full description for the Probabilistic Storm Surge Exceedance product at MDL's web page.
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