Vortex Data Message
One type of data that is helpful with determining the strength of a hurricane is a Vortex Data Message. When Hurricane Hunters fly into a hurricane, they send a specifically coded message of observations from the hurricane’s eye to the National Hurricane Center. This message passes along vital information of the strength and demeanor of the hurricane, which in turn helps to increase forecast accuracy.
At 2350Z on September 14th, 2004, the Vortex Data Message for Hurricane Ivan read:
|
URNT12 KNHC 142350 |
Broken down, this would translate to:
| URNT12 KNHC 142350 VORTEX DATA MESSAGE |
The first line of the Vortex Data Message contains the code used to identify it in meteorological data bases. It also gives the date and time the message was transmitted, which would be on the 14th day of the month (September of 2004) at 2350Z. |
| A. 14/2319Z | Line A is the time when the center of the hurricane was located. Much like the previous line, it uses the same date and time format. Therefore, the report of when Ivan’s center was located is from the 14th day of the month at 2319Z. |
| B. 24 DEG 33 MIN N 86 DEG 56 MIN W |
Line B is the latitude and longitude of the center of the hurricane. According to the message, Ivan’s eye was located at 24° 33’ N and 86° 56’ W. |
| C. 700 MB 2491 M | Line C is the minimum height at standard level (700-mb for hurricanes). For Ivan, on this particular message, the minimum height at 700-mb was 2491 meters which is considerably lower than the typical 700-mb standard height of 3011 meters. This contrast indicates significant low pressure and just how intense Ivan was. |
| D. N/A | Line D is the estimated maximum surface wind observed in knots. When Hurricane Hunters fly into a hurricane, the flight meteorologist is able to estimate how strong the surface wind is by the appearance of the sea surface. However, on this particular message for Ivan, the estimated maximum surface wind is not applicable. This is likely due to darkness, heavy rain, or clouds which can obstruct the sea surface from view of the flight meteorologist. |
| E. N/A | Line E is the direction (in degrees and nautical miles) from the center of the hurricane where the maximum surface wind was seen. On the message for Ivan, this is also not applicable since the maximum surface wind in line D was unable to be observed. However, if the maximum surface wind had been observed, this line would have given the direction (in degrees) where the maximum surface winds were observed in relation to the hurricane’s center, as well as how far (in nautical miles) it was from the center. |
| F. 354 DEG 116 KT | Line F is the maximum flight level wind near the hurricane’s center. This is the highest wind speed and direction measured by the aircraft’s instruments on the last 100 mile leg inbound to the storm. However, if the observed outbound winds are higher than the reported inbound winds, they will be reported instead. If the message had already been transmitted prior to observing faster outbound winds, then a corrected message would be sent with the maximum outbound winds reported in line P. The reported maximum flight level winds for Hurricane Ivan at the time of the message is 116 knots at 354°, or almost north. |
| G. 258 DEG 19 NM | Line G is the direction (in degrees and nautical miles) from the center of the hurricane where the maximum flight level winds are observed. At the time of the message, the maximum flight level winds were located at 258°, or west-southwest, and 19 nautical miles from Ivan’s center. |
| H. 928 MB | Line H is the minimum sea level pressure, computed by either a dropsonde or extrapolation from aircraft sensor information. Ivan’s minimum sea level pressure at the time of the message was 928 mb. Since the word “EXTRAP” doesn’t precede the pressure reading, the pressure was measured by a dropsonde which is usually more accurate. If the word “EXTRAP” had preceded the pressure reading, that would indicate that the pressure had been measured by extrapolation. |
| I. 13 C/ 3054 M | Line I is the maximum flight level temperature and pressure altitude outside the hurricane’s eye. Outside Ivan’s eye at the time of the message, the temperature was 13°C at an altitude of 3054 meters. |
| J. 19 C/ 2992 M | Line J is the maximum flight level temperature and pressure altitude inside the hurricane’s eye. This temperature is used in contrast to the temperature outside the hurricane’s eye from Line I. The difference between the two gives an idea of just how strong the hurricane is. The greater the difference in temperature, the stronger the hurricane is. Inside Ivan’s eye, the temperature was 19°C at an altitude of 2992 meters. This is 6°C warmer than the temperature outside the eye which is a fairly significant contrast and indicates that Ivan was a healthy storm at the time. |
| K. 16 C/ N/A | Line K is the dew point temperature and sea surface temperature inside the hurricane’s eye. The closer the dew point is to the air temperature inside the eye, the higher the relative humidity is. A high relative humidity indicates a possibility of clouds being present inside the eye which is a sign of weakening. Inside Ivan’s eye, the dew point temperature was 16°C. The second part of line K, sea surface temperature, is no longer used which is why it reads not applicable. |
| L. OPEN SW | Line L is the description of what the eye of the hurricane looks like on radar. At the time of the message, Ivan’s eyewall was open to the southwest. |
| M. C43 | Line M is the shape of the hurricane’s eye and diameter (in nautical miles). The shape of a hurricane’s eye is coded with either a C (circular), CO (concentric), or E (elliptical). Ivan’s eye was circular with a diameter of 43 nautical miles. |
| N. 12345/7 | Line N is how the center of the storm was determined and the level it was found at. The first part of line N contains a series of numbers ranging from 1 to 5, with each number corresponding to a means used to find the hurricane’s center. These means are: Penetration (1), Radar (2), Wind (3), Pressure (4), Temperature (5). According to the message, Ivan’s center was found by 12345, meaning all the means were used to locate it. The second part of line N is the pressure level that the center of the hurricane was found. Ivan’s center was found at 7, which translates to 700-mb. |
| O. 1/1 NM | Line O is an estimate of the Navigation and Meteorological Accuracy for the position of the hurricane’s center (in nautical miles). The Navigation Accuracy (first number) is a gauge of how well the navigational equipment is operating and the Meteorological Accuracy (second number) depends on how well the hurricane’s center can be defined by the meteorological data. The Navigation and Meteorological Accuracy numbers for Ivan at the time of the message were 1/1 nautical miles. |
| P. NOAA3 3609A IVAN OB 25 MAX FLT WND 147KTS NE QUAD 2039Z |
Line P is the flight meteorologist’s remarks about the hurricane. The first part of line P is the Mission ID. On this message, the Mission ID for Ivan is: NOAA3 3609A IVAN OB 25. This translates to: NOAA (National Oceanic and Atmospheric Agency) aircraft #3 is flying the 36th mission on Hurricane Ivan, which is the 9th tropical cyclone in the Atlantic. The next part of line P for this message reads as follows: MAX FLT WND 147KTS NE QUAD 2039Z. This remark means that while the highest wind was seen prior to reaching the center of the hurricane this time around (116 knots; Line F), a stronger fight level wind of 147 knots was seen in the northeast quadrant of the hurricane at 2039Z. |
As can be seen by the message above, Vortex Data Messages contain quite a bit of useful data that helps with assessing the strength of a hurricane. When combined with previous messages of a particular hurricane, it can indicate patterns in weakening and strengthening within the storm.
An example of this would be the trend in Hurricane Ivan’s eyewall (Line L). When a hurricane’s eyewall is closed, a band of intense thunderstorms surrounds the eye in a solid ring. This is a sign of a powerful hurricane and a possible indication of further strengthening. When there is a break in the eyewall, meaning that the eyewall is open, this is a sign of weakening within the storm. Throughout the day of September 14th, 2004, Ivan’s eyewall varied between being closed and open according to previous Vortex Data Messages. It was during this time that Ivan was weakening from a Category 5 hurricane to a Category 4. This suggests that the varying trend in the structure of the eyewall throughout the day is a possible indicator of the storm losing some of its strength.
Scatterometry
Another type of data that is helpful with determining the strength of a hurricane, particularly if the storm is out of range of reconnaissance aircraft, is Scatterometry. Scatterometers are high frequency radars mounted on satellites that measure near-surface wind speeds and directions over the oceans. To do this, scatterometers use pulses of microwaves with relatively short wavelengths and measure the backscatter from the ocean. Since scatterometers can measure near-surface winds regardless of weather conditions, this makes them useful in assessing the winds of any tropical cyclone, hurricanes in particular. Scatterometers can also be helpful in detecting circulations of cyclonic winds that have the potential to develop into tropical cyclones many hours in advance of them reaching tropical depression status.
A Scatterometry image of Hurricane Ivan at 2359Z on September 14th, 2004. The image indicates a maximum reliable wind speed of 115 knots. (Courtesy of the Remote Sensing Systems.)
The Scatterometry image of Hurricane Ivan, taken at 2359Z on September 14th, 2004, shows a definite pattern of cyclonic winds around the center of the storm. According to the image, the maximum reliable wind observation is 115 knots. Some of the wind vectors are suspect and may not be reliable. The heavy precipitation that often falls in tropical cyclones can contaminate the accuracy of the winds measured by scatterometers by decreasing the transmitted signal strength from either scattering or absorbing the microwaves. Wind vectors that are suspected to be unreliable are marked with a gray dot at the end, as can be seen on the image.
HRD Wind Analysis
When hurricanes in the Atlantic pose a threat to land, forecasters use a HRD Wind Analysis to assess the wind speeds within the storms. The wind speed data that makes up this analysis is collected by several different sources. The sources used to create the HRD Wind Analysis for Hurricane Ivan at 00Z on September 15th, 2004 were a GPS dropwindsonde, a moored buoy, a C-MAN station, QSCAT (which is a scatterometer), a ship, GOES-SWIR, and SFMR43.
The HRD Wind Analysis of Hurricane Ivan at 00Z on September 15th, 2004 indicates the strongest area of winds to be to the east and northeast of Ivan's eye. (Courtesy of the Hurricane Research Division.)
The 00Z HRD Wind Analysis of Hurricane Ivan shows the strongest area of winds to be just to the east and northeast of Ivan’s eye. According to the analysis, the observed maximum surface wind was 121 knots and located 21 nautical miles northeast of the center. This observation is based on the SFMR43’s surface measurement. A Stepped Frequency Microwave Radiometer (SFMR) is a passive remote sensor that senses surface wind speeds and is mounted on reconnaissance aircraft. The observed maximum surface winds are very close to the HRD’s analysis of maximum analyzed winds of 120 knots, located 23 nautical miles northeast of the center. These winds would fall into Category 4 strength, indicating just how intense Ivan was at the time.
