How can I decode the lowest one-minute pressure and peak one-minute winds?
The Tropical Prediction Center (TPC) has funded the National Data Buoy Center (NDBC) to change the software on their buoys to report the highest one-minute wind and the lowest one-minute pressure observed in the last hour. This will provide improved temporal sampling of key measurements that will more closely match the averaging times of wind and pressure implicit in TPC's forecasts. Selected buoy stations will be deployed with this capability early in the summer of 2005.
The additional information that these buoys will transmit each hour is as follows:
|Highest one-minute mean wind speed||m/s to nearest m/s|
|Direction of one-minute peak wind||nearest ten degrees|
|Time of one-minute peak wind||nearest minute|
|Lowest one-minute average pressure||nearest 0.1 hPa|
|Time of one-minute pressure||nearest minute|
Because of power system constraints the barometer cannot be left on continuously for the entire deployment. Therefore, the lowest one-minute pressure will only be reported when the last hourly pressure is less than 1009 hPa. This value may be adjusted downward for buoys deployed in the mid- or high-latitudes.
These measurements will be placed in Section 5, which is the national section of the code that begins with "555". This would have minimal, if any, potential impact on existing software decoders.
The following groups will be added to Section 5 of C-MAN and U.S. fixed buoy (i.e. FM-13) reports:
|5plplplpl||plplplpl is the lowest pressure during the previous hour, in tenths of hPa. This group shall only be reported when the pressure is less than 1009 hPa. Otherwise, the group will be missing. When pressure exceeds 1000 hPa, the leading "1" will be dropped. For example, 1004.2 hPa will be coded as 50042.|
|7hhmm||hhmm is the hour and minute (UTC) of the lowest pressure during the previous hour|
|8ddff or 8ddfff||dd is true direction, in tens of degrees, from which the highest peak one minute wind during the previous hour was blowing. For fixed buoys, ff is the associated speed, in units indicated by iw. For C-MAN reports, fff is the associated speed in knots.|
|9hhmm||hhmm is the hour and minute (UTC) of the highest peak one-minute wind during the previous hour|
Existing national practices code groups
For reference purposes, the following groups are currently being reported (when data are available) within Section 5 of C-MAN and U.S. fixed buoy reports:
|11f10f10f10||f10f10f10 is the 10-meter extrapolated wind speed, in units indicated by iw|
|22f20f20f20||f20f20f20 is the 20-meter extrapolated wind speed, in units indicated by iw|
|3GGgg||Time of observation (in hours and minutes UTC) of peak 5-second wind during the previous hour|
|4ddfmfm or 4ddfmfmfm||dd is true direction, in tens of degrees, from which peak 5-second wind is blowing; if report is from a fixed buoy, fmfm is peak 5-second wind speed during the previous hour, in units indicated by iw. If report is from a C-MAN, fmfmfm is peak 5-second wind speed during the previous hour, in units indicated by iw.|
|6GGgg||End time (in hours and minutes UTC) of the most recent 10-minute average continuous wind measurement.|
|Direction in whole degrees and speed of the continuous wind data, taken 10 minutes apart, starting during the preceding observation hour. If iw indicates knots, speeds here are in knots. If iw indicates meters per second, speeds here are tenths of meters per second.|
|TIDEHtHtHtHt||HtHtHtHt is the 6-minute average water level, above/at/below Mean Lower Low Water (MLLW), ending at the top of the hour, in hundredths of feet. If water level is at or above MLLW, 1000 is added to the water level (in hundredths of feet) for encoding; i.e. an HtHtHtHt of 1132 means the water level is 1.32 feet above MLLW. Water level at MLLW would be encoded as 1000. If water level is less than MLLW, the height (in hundredths of feet) is subtracted from 1000 prior to encoding. i.e. HtHtHtHt of 0832 is 1.68 feet below MLLW (1000 - 0168 = 0832).|