The National Hurricane Center building

The National Hurricane Center is the division of the National Weather Service that maintains a continuous watch on tropical cyclones in the Atlantic and Eastern Pacific Oceans. Specifically, their mission is described as, to save lives, mitigate property loss, and improve economic efficiency by issuing the best watches, warnings, forecasts and analyses of hazardous tropical weather, and by increasing understanding of these hazards. [1]

Graphical Tropical Weather Outlook

The Graphical Tropical Weather Outlook, also known as the GTWO, is a graphic generated by the National Hurricane Center every 6 hours starting at 2 AM EDT everyday during the hurricane season, and sometimes outside of the season if needed. The GTWO shows an overlay of suspect areas of formation and tropical cyclones over an infrared image of the Atlantic or East Pacific basins and was first generated on June 8, 2009.


Hurricane Season Tropical Cyclone Reports

Subsequent to every tropical cyclone season, the National Hurricane Center issues a Tropical Cyclone Report (formerly Preliminary Report) on every tropical cyclone in its jurisdiction. The Tropical Cyclone Reports contain comprehensive information on each tropical cyclone, including synoptic history, meteorological statistics, casualties and damages, and the post-analysis best track (six-hourly positions and intensities).[2] From 1995 to the present year, the yearly archives include a colored track map of the storms in the season.

Prior to 1995 in the Atlantic, the archive extends to 1958, with reports provided on most storms through sub-folders. From 1991 to 1995, as well as from 1958 to 1965, the archive includes additional reports on marine advisories, the operational track, local damage reports, public advisories, recon fixes, and discussions; not every storm has all of the aforementioned reports. The archive in the Pacific ocean extends from 1988 to 1996, and includes most of the previously mentioned reports.

Hurricane Season Tropical Cyclone Advisory Archive

The center issues forecast advisories, discussions, and strike probabilities for all operationally classified tropical cyclones from 1998 to the present year. Public advisories are issued for all Atlantic tropical cyclones, and for all Pacific tropical cyclones in their jurisdiction that threaten land.

Hurricane Season Tropical Cyclone Monthly Summary Archive

At the end of every month, the center issues a summary of the monthly activity for each basin. It has been issued for both the Atlantic Ocean and the eastern Pacific Ocean since 1999, and covers every operationally classified tropical or subtropical cyclone during the month. The November summary covers the tropical activity for the entire season. Two summaries are different from the rest; the July 1999 Atlantic summary contained a tropical wave that approached developing into a tropical cyclone, and the June 2003 Atlantic summary includes a tropical storm that formed in April.


Public Advisories

Public advisories are normally issued at 6 hour intervals at 5:00 AM/PM and 11:00 AM/PM, but dangerous storms and storms nearing landfall may be issued public advisories every 3 hours, which would include the times of 2:00 AM/PM and 8:00 AM/PM. Public advisories first contain one or two sentences that outline the changes with the new advisory. After that, there is a summary regarding the current parameters of a tropical system. They include its absolute location, relative location, maximum sustained winds, present movement, and minimum central pressure. If the storm is expected to affect land, a section for watches and warnings outline the current warned areas and any changes. Following the watches and warnings section is a section that contains a short paragraph discussion on the tropical system and the 48-hour outlook for it. If land is expected to be affected, like the watches and warnings section, a "Hazards affecting land" section may be included, outlining the dangers that the tropical system may present to land. The final section regards the time of the next advisory.

Forecast Advisories

Forecast advisories contain the summary section included in a public advisory and the watches and warnings section if the storm is expected to affect land. However, this advisory also contains forecast information for the future track of a tropical system. It contains the time of forecast, forecast coordinates, forecast wind speeds, and forecast wind fields.


Discussions contain current information on the progress of the storm. Discussions contain meteorologically intricate language. They usually contain 3 sections. The first section normally regards what has occured in the past few hours since the last advisory and the strength of the tropical system. The second section normally outlines what factors were incorporated to create the official NHC forecast. The last section shows the forecast positions of the tropical system.

Wind Speed Probabilities

Wind Speed Probabilities show the forecast wind speeds of a tropical system and the chances of the system potentially reaching benchmark strengths like tropical storm or hurricane strength. The WSP first shows current information on the tropical cyclone and background information such as converting Zulu time into a local time zone. The wind speed probability is displayed a graph. The graph is sorted into Saffir-Simpson hurricane scale probability versus time. Percentages are given for each hurricane "rank" at a certain time which can be found at the top of the graph. If the probability is 0%, it is represented as an X. Below the graph shows the forecast wind speed for the specific time. Following that is another set of instructions and background infromation. The final section shows the probability of wind speeds at a certain time at different locations. At the top is the forecast time and date. Below that are the probabilities. On the left are select locations. Below each forecast time are a set of 2 numbers. The first number is a benchmark wind speed, and the second number is the probability of that wind speed occuring at the specified time and at the specified location. Multiple benchmmark wind speeds may be assigned to a location. There are up to 3 benchmark speeds that can be used. They are tropical storm force (34 kt), gale force (50 kt), and hurricane force (64 kt). Below is an example.

              FROM    FROM    FROM    FROM    FROM    FROM    FROM 
 TIME       12Z SAT 00Z SUN 12Z SUN 00Z MON 12Z MON 12Z TUE 12Z WED
               TO      TO      TO      TO      TO      TO      TO
            00Z SUN 12Z SUN 00Z MON 12Z MON 12Z TUE 12Z WED 12Z THU

FORECAST HOUR   (12)    (24)    (36)    (48)    (72)   (96)    (120)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
SAVANNAH GA    34  3  16(19)  10(29)   5(34)   5(39)   3(42)   1(43)
SAVANNAH GA    50  X   X( X)   2( 2)   2( 4)   3( 7)   X( 7)   1( 8)
SAVANNAH GA    64  X   X( X)   1( 1)   X( 1)   X( 1)   X( 1)   X( 1)

In this example we used the probability for Savannah, GA, in Subtropical Storm Beryl's (2012) 3rd advisory. It shows that at the specified time from 12Z Saturday to 00Z Sunday, Savannah, GA has a 3% chance for tropical storm force winds and a 0% chance for gale or hurricane force winds. If we go all the way to 36 hours out, from 12Z Sunday to 00Z Monday, we see that there is a 10% chance for tropical storm force winds, a 2% chance of gale force winds, and a 1% chance for hurricane force winds. The number in parentheses shows the probability that the specified threshold strength has been reached before. For example, at 120 hours out, from 12Z Wednesday to 12Z Thursday, there would've been a 43% chance that tropical storm winds has been reached in the past.

External links

National Hurricane Center's website