Reports from the National Data Buoy Center’s Stations During the Passage of Hurricane Flossie in the Eastern and Central Pacific
08 – 16 August 2007
Although Flossie did not set any extreme records at any of NDBC’s stations, it was unique in that it is the first time that a single tropical cyclone passed within 300 nautical miles (NM1) of NDBC’s three types of moored buoy ocean observing systems – weather buoys (51004, 51002, and 51003), deep-ocean tsunameter (51407), and the Tropical Atmosphere-Ocean Array (TAO station 51006) (Figure 1). Initially a powerful tropical cyclone, it remained small and then weakened rapidly as it moved south of Hawai’i2 .
By passing nearly over the top of station 51002, Flossie set extreme records for sea-level pressure, wind speed, and gusts (Figure 2) for August at station 51002 (Period of Record: September 1984 – August 2007). 51002’s minimum sea-level pressure of 1004.6 hPa was the lowest pressure for any month since January 1996. The 5.4 m wave height at 51004 was just shy of the August record of 5.5 m for that station (Figure 6).
1 The significance of 300 NM is that the tropical cyclone advisories request 3-hourly observations from
ships within 300 NM of a tropical cyclone center. Track information is based on the positions given in the
Figure 1: Flossie's Preliminary Track and NDBC Stations
Figure 2: Wind and Pressure at 51002
Figure 3: Wave Heights and Dominant Period at 51002
51002 also takes near-surface current measurements. During the passage of Flossie, 51002 reported the highest eastward speeds of the year (Figure 4) of more than 40 cm/sec.
Figure 4: Eastward Near-Surface Currents (SCMUV1), positive values are towards the east.
Link to Station Page: http://www.ndbc.noaa.gov/station_page.php?station=51002
Figure 5: Winds and Pressure at 51004
Figure 6: Wave Heights and Dominant Periods at 51004
Link to Station Page: http://www.ndbc.noaa.gov/station_page.php?station=51004
Figure 7: Winds and Pressure at 51003
Figure 8: Wave Height and Dominant Period at 51003
Link to Station Page: http://www.ndbc.noaa.gov/station_page.php?station=51003
The first NDBC station within 300 NM of Flossie was the TAO Station 51006 at 9°N 140°W. The closest point of Flossie’s approach to 51006 was approximately 219 NM to the north at 1100Z on 11 August 2007. NDBC receives hourly wind speed data from TAO Stations (Figure 9). The wind speeds are two-minute averages.
Figure 9: Wind Speed at TAO Station 51006
Lastly, Flossie passed 128 NM to the south the NDBC deep-ocean tsunameter at Station 51407, which is 140 NM southeast of Honolulu, at approximately 0900Z on 15 August 2007, although the water-column heights are unremarkable (Figure 10) given the small size of Flossie. The tsunameter measures pressure on the sea floor then converts the pressure to the height of the water column.
Figure 10: Estimated Water-Levels (MLLW) from Tsunameter 51407
Explanation of Terms
Acknowledgement: Dawn C. Petraitis provided hourly TAO data.