Request for Comments - Tropical Cyclone Discussion

---

The National Hurricane Center (NHC) issues a number of text products with every tropical cyclone advisory package. One of these products is the Tropical Cyclone Discussion (TCD), which describes the reasoning behind the forecaster's analysis and forecast of a tropical cyclone. It will typically discuss the observations justifying the analyzed intensity of the cyclone, a description of the environmental factors expected to influence the cyclone's future track and intensity, and a description of the numerical guidance models. It may also describe the forecaster's degree of confidence in the official forecast, discuss possible alternate scenarios, and highlight unusual hazards. The product also includes a table of forecast positions and intensities out to 120 h. An example of the TCD is given below.

NHC is soliciting feedback from users on whether the current form and content of the TCD meets their needs. Suggestions for improvements in the product are welcome, and you may submit the feedback form located below the following example.

Example of a Tropical Cyclone Discussion

HURRICANE KATRINA DISCUSSION NUMBER  16
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
500 AM EDT SAT AUG 27 2005
 
THE EYE HAS BECOME CLEARLY DISCERNIBLE DURING THE PAST FEW HOURS IN
GOES-12 INFRARED IMAGERY.  AIRCRAFT RECONNAISSANCE INDICATES THE
MINIMUM CENTRAL PRESSURE IS FALLING... MOST RECENTLY MEASURED AT
945 MB.  WHILE SUCH A LOW PRESSURE IS TYPICAL OF SOME CATEGORY FOUR
HURRICANES...THE MAXIMUM 700 MB FLIGHT LEVEL WINDS HAVE NOT YET
EXCEEDED 104 KT...WHICH CORRESPONDS TO ABOUT 95 KT AT THE SURFACE. 
GIVEN THE FALLING PRESSURE...AND DVORAK INTENSITY ESTIMATES
RANGING FROM 100 TO 115 KT...THE ADVISORY INTENSITY WILL BE
INCREASED TO 100 KT...MAKING KATRINA A CATEGORY THREE HURRICANE. 
THE AIRCRAFT DATA AND A FEW SURFACE OBSERVATIONS ALSO INDICATE THAT
KATRINA HAS GROWN IN SIZE... WHICH PERHAPS EXPLAINS WHY THE MAXIMUM
WINDS HAVE NOT YET CAUGHT UP TO THE CENTRAL PRESSURE.  THE INITIAL
AND FORECAST WIND RADII HAVE BEEN EXPANDED ACCORDINGLY.
 
WSR-88D RADAR IMAGERY FROM KEY WEST...AND THE SERIES OF AIRCRAFT
FIXES... INDICATE THAT KATRINA IS WOBBLING ABOUT A HEADING JUST
SOUTH OF DUE WEST...SO THE LONG-ANTICIPATED TURN TO THE WEST MIGHT
BE STARTING.  THE DYNAMICAL MODELS ALL FORECAST A
WEST-NORTHWESTWARD MOTION TO BEGIN LATER TODAY...FOLLOWED BY A
GRADUAL TURN TOWARD THE NORTHWEST AND NORTH DURING THE NEXT 2-3
DAYS AS THE RIDGE TO THE NORTHWEST OF KATRINA EASES WESTWARD AND A
WEAKNESS DEVELOPS OVER THE NORTHERN GULF.  THE DYNAMICAL MODEL
CONSENSUS FORECAST OF THE TRACK THROUGH THE GULF OF MEXICO HAD
SHIFTED WESTWARD DURING THE PAST 24 HOURS OF FORECAST CYCLES.  THE
LATEST CONSENSUS TRACK IS ONLY SLIGHTLY WEST OF THE PREVIOUS... SO
IT IS POSSIBLE THAT THE WESTWARD SHIFTING OF THE MODELS IS ENDING. 
THE NEW OFFICIAL FORECAST IS RIGHT ON TOP OF THE CONSENSUS TRACK
AND A BIT TO THE WEST OF THE PREVIOUS ADVISORY.  DUE TO THE
DECREASING SPREAD IN THE MODELS... THE CONFIDENCE IN THE FORECAST
TRACK IS INCREASING.
 
KATRINA IS LOCATED WITHIN AN ATMOSPHERIC ENVIRONMENT THAT SEEMINGLY
CANNOT GET MUCH MORE CONDUCIVE FOR STRENGTHENING...PRIMARILY DUE
TO A VERY LARGE UPPER-LEVEL ANTICYCLONE OVER THE ENTIRE GULF OF
MEXICO.  NOT SURPRISINGLY...UPPER-LEVEL OUTFLOW FROM THE HURRICANE
CONTINUES TO BECOME MORE ESTABLISHED.  THIS WEAK WIND SHEAR
ENVIRONMENT IS FORECAST BY THE DYNAMICAL MODELS TO PERSIST FOR
ABOUT THE NEXT THREE DAYS UNTIL AN UPPER-LEVEL TROUGH MOVES INTO
TEXAS FROM THE WEST.  THEREFORE SHEAR COULD BEGIN TO INCREASE OVER
THE HURRICANE NEAR THE TIME IT MAKES LANDFALL ON THE
NORTHERN GULF COAST... BUT IT SEEMS THAT WILL BE TOO LATE TO
PREVENT KATRINA FROM MAINTAINING MAJOR HURRICANE STATUS AT
LANDFALL.  THE SHIPS GUIDANCE NOW SHOWS STRENGTHENING TO 123 KT...
AND THE OFFICIAL FORECAST NOW PEAKS AT 120 KT OVER THE NORTHERN
GULF WITHIN THE NEXT COUPLE OF DAYS.
 
THE 12-FOOT SEAS RADII HAVE BEEN EXPANDED BASED UPON DATA FROM NOAA
BUOY 42003 AND ON SHIP DATA.
 
FORECASTER KNABB
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/0900Z 24.4N  84.4W   100 KT
 12HR VT     27/1800Z 24.5N  85.4W   105 KT
 24HR VT     28/0600Z 25.0N  87.0W   115 KT
 36HR VT     28/1800Z 26.0N  88.7W   120 KT
 48HR VT     29/0600Z 27.4N  89.9W   120 KT
 72HR VT     30/0600Z 31.5N  90.0W    75 KT...INLAND
 96HR VT     31/0600Z 36.0N  87.5W    30 KT...INLAND
120HR VT     01/0600Z 40.0N  82.0W    25 KT...EXTRATROPICAL

Your Name (optional):
Email (optional):
Please enter your comments in the box below.
Required:  Please type the characters "three" in the box (We require this step to help prevent form spam)
All comments are delivered directly to the NHC.