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

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.  In this case, the 700mb height was 2490 m which is much below the standard value of 3011 m, making Ivan a strong storm.

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.  No estimate of surface winds was made on this flight.

Maximum Flight Level Wind Near Ivan'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 119 kt winds bearing 43 degrees, or northeast, from Ivan's center.

Maximum Flight Level Wind Bearing/Range From Ivan's Center: the direction and distance (in nautical miles) of maximum flight level wind.  The maximum winds, with a bearing of 307 degrees, northwest,  were encountered 25 nm from the storm's center.

Minimum Sea Level Pressure: is determined by either instruments on board the aircraft or a device (dropsonde) dropped into the storm's center.  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. In this case, 931 mb represents a very healthy storm.

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.

Maximum Flight Level Temperature / Pressure Height Inside The Eye:   Temperature differences between the environment inside and outside the eye are a key indicator of hurricane intensity. Here, the difference between I & J is 5 degrees, indicating a relatively strong storm. When Ivan was at its strongest, a category 5, the difference was 13 degrees.One of the interesting things about a hurricane is that the eye is supposed to be warmer because it's a warm core storm. The height difference at 700mb was only eight meters.

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. In this case, the temperature inside the eye of 16 C, line J, compared with the dewpoint of 10 C gives a relative humidity of 68%. This means the conditions inside the eye were probably clear, indicative of a strong storm.  Sea surface temperatures are no longer collected.

Eye Character:  this data is collected visually by the onboard meteorologist.  Ivan's eye was observed to be a "closed wall" indicating the eye was completely surrounded by a ring of thunderstorms.

Eye Shape/Orientation/Diameter:  Eye shape is reported using codes where C = circular, CO = concentric and E = elliptical.  Ivan's eye was reported as circular.  The second value listed in the message -- 40 -- was the size of Ivan'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. Ivan's eye was relatively large. In the strongest of storms, the eye is much smaller.

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 temperature 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, Ivan's center was fixed at the 700mb level.

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.  The "Meteorological Accuracy" depends on how well the storm center can be defined by the meteorological data: if there is a sudden, sharp wind shift, and the temperature peak and pressure drop all coincide, the met accuracy will be a small number which is the case with Ivan. A weaker storm will probably have a larger met accuracy.

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.  Here, the pilot was discussing flight level winds and temperature as well as the eye.