Decoding a Vortex Message


Description   Vortex Data
Message Header: the identification number of the message and the data and time of transmission.  In this case, the message was transmitted at 0544Z (1:44AM) on the 13th.   URNT12 KNHC 130544
Fix Date/Time:  the date and time that the center of the storm was located.  Charley's center was fixed at 0540Z (1:40AM) on the 13th.   A:  13/0540Z

Latitude & Longitude: the location of Charley's center at the time of message.


B:  22 Deg 57 Min N

     82 Deg 38 Min W

Minimum Height at Standard Level: the height (in meters) at which the specified pressure (in millibars) was observed.  This observation is compared to standard values to determine the overall strength of the storm.  This value is not reported if the flight was below 1500 feet, which is the case here.


C:   NA

Maximum Surface Wind (Estimated): the onboard meteorologist visually examines the surface of the ocean on the inbound flight to estimate the winds in knots.  In this instance an estimate was not made, most likely due to darkness.


D:   NA

Maximum Surface Wind Bearing/Range From Center (Estimated): the compass heading and distance (in nautical miles) from the center of the surface winds reported in section D.  Again, no estimate of surface winds was made on this flight.


E:   NA

Maximum Flight Level Wind Near Charley's Center: the velocity (in knots) and the compass heading of maximum flight level wind during the last 100 miles into the storm.  The flight crew noted 85 kt winds bearing 46 degrees, or northeast, from Charley's center.


F:   046 Deg 085 KT

Maximum Flight Level Wind Bearing/Range From Charley's Center: the direction and distance (in nautical miles) of maximum flight level wind.  The maximum winds, with a bearing of 290 degrees (nearly northwest) were encountered 10 nm from the storm's center.


G:   290 Deg 10 NM

Minimum Sea Level Pressure: is determined by either instruments on board the aircraft or a device (dropsonde) dropped into the storm's center.  I can't explain the absence of an observation and it seems unlikely that both forms of measurement failed on this flight.  Sea level pressure (in millibars) is used to determine the strength of a storm and the trend in intensity.  A decline in sea level pressure indicates a strengthening (deepening) storm.


H:   NA

Maximum Flight Level Temperature / Pressure Height Outside The Eye: a comparison of these values with those from inside the storm provide meteorologists with a clue as to the storm's strength.


I:  5 C / 3085 M

Maximum Flight Level Temperature / Pressure Height Inside The Eye: in this instances no temperature reading was available within the eye.  The height difference at 700mb was only two meters.  Temperature differences between the environment inside and outside the eye are a key indicator of hurricane intensity.


J:   NA / 3083 M

Dewpoint Temperature / Sea Surface Temperature Inside The Eye: the dewpoint and temperature are used to calculate the eye's relative humidity. This allows meteorologists to determine if the eye is clear of filled with clouds.  No dewpoint temperature was collected on this flight, suggesting a malfunction of the sensor. Sea surface temperatures are no longer collected.


K:   NA / NA

Eye Character:  this data is collected visually by the onboard meteorologist.  NA is reported if an eye is not present or is not at least 50% surrounded by wall clouds.  Charley's eye was observed to be a "closed wall" indicating the eye was completely surrounded by a ring of thunderstorms.


L:  Closed Wall

Eye Shape/Orientation/Diameter:  Eye shape is reported using codes where C = circular, CO = concentric and E = elliptical.  Charley's eye was reported a circular.  The second value listed in the message -- 18 -- was the size of Charley's eye in nautical miles.  The size of a hurricane's eye and the change of size over time is yet another indicator of the storm's health.


M:   C18

Fix Determined By / Fix Level: This first part of the observation (before the slash) indicates the methods used to locate the center of the storm.  The presence of a code indicates that the method was used with 1 = penetration, 2 = radar, 3 = wind, 4 = pressure and 5 = temperature.  In this instance all methods but penetration were used.  The second part of the observation indicates the pressure level used to determine the center with 0 = surface (<= 1500ft), 2 = 200mb, 3 = 300mb, 4 = 400mb, 5 = 500mb, 6 = 600mb, 7 = 700mb, 8 = 800mb, or 9 = 925mb.  On this date, Charley's center was fixed at the 700mb level.


N:   2345 / 7

Navigation Fix / Meteorological Accuracy: These observations provide an estimate of the accuracy of the aircraft's navigation system, as well as, the accuracy of the meteorological data used to fix the storm's center.  At this time the navigation system was accurate to within .1 nautical mile.  No report was provided for meteorological accuracy in this instance.


O:   0.1 / NA NM

Remarks Section: This section first presents the mission id number and the name of the storm.  Additional remarks are at the discretion of the meteorologist and may include references to unusual features.


P:   AF980 0803A  Charley OB 06

      Max Fl Wind 85 KT NW quad

      0538Z. Radar estimate of center

      over Cuban Coast.  Max Fl wind

      outbound thru NE quad 102 KT