Coastal Watches/Warnings and Forecast Cone for Storm Center

cone graphic

* If the storm is forecast to dissipate within 3 days, the “Full Forecast” and “3 day” graphic will be identical

Click Here for a 5-day Cone Printer Friendly Graphic

How to use the cone graphic (video):

Link to video describing cone graphic

About this product:

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, when selected, 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.

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 Wind History graphic linked above.

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

tabular form for selected locations and forecast positions
. This information is also presented in
graphical form for the 34 kt, 50 kt,
and 64 kt thresholds.

Note:  A detailed definition of the NHC track forecast cone is also available.

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Tropical Depression Twenty-One-E Forecast Discussion

WTPZ41 KNHC 180833

Tropical Depression Twenty-One-E Discussion Number   9
NWS National Hurricane Center Miami FL       EP212019
300 AM CST Mon Nov 18 2019

Organized deep convection had been sparse for a few hours, but some
cold cloud tops have recently developed near the estimated center
location. Infrared imagery shows a much larger area of deep
convection farther to the north and northeast, but this feature
lacks curvature and doesn't seem to be directly associated with the
depression's circulation. A partial ASCAT-A pass around 0315Z showed
only 15-20 kt winds to the east of the center, but the initial
intensity is being held, perhaps generously, at 25 kt since the
entire circulation was not sampled. The NHC forecast shows the
system becoming a remnant low by 24 hours, and while the global
models show the circulation dissipating by 72 h, it wouldn't be
surprising if this happened much sooner.

The center has been difficult to track in infrared imagery, but
based on the earlier scatterometer data and the latest satellite
fixes, the initial motion estimate is 305/06. The system should be
steered generally westward from now until dissipation by a weak
low-level ridge to the north. The new NHC forecast lies near the
north edge of the guidance envelope close to HCCA and the GFS.


INIT  18/0900Z 12.2N 105.0W   25 KT  30 MPH
 12H  18/1800Z 12.3N 105.8W   25 KT  30 MPH
 24H  19/0600Z 12.4N 106.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 36H  19/1800Z 12.5N 107.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 48H  20/0600Z 12.5N 108.8W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  21/0600Z...DISSIPATED

Forecaster Brennan

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