Using ASCAT Wind and Other Data in Marine Forecasting

4.0 Forecast Future Conditions at a Projected Point » 4.13 WW III Forecast and the Polarstern

At 06 UTC on 24 November, WAVEWATCH III was forecasting a large zone of “very rough to high” seas approaching the position of the Polarstern (the white dot) from the west. The forecast probable wave height was approaching 5.5 m (increasing to 10 to 12.5 m in the area indicated in brown). By 09 UTC, the Polarstern was expected to reach the edge of this area.

WAVEWATCH III model forecast for 06 UTC 24 November 2013 with position of Polarstern marked

At the 09 UTC synoptic hour on 24 November, the Polarstern was reporting wind waves of 4.5 m due to the increased wind activity and a swell of 3.5 m. This would lead to expected total seas of up to 8 m.

WAVEWATCH III model forecast for 09 UTC 24 November 2013

The wind speed continued to increase through the morning, and the pressure tendency showed a decreasing trend as the vessel was still approaching the front.

By 15 UTC on 24 November, the vessel was reporting severe gale force west-northwesterly winds (41 to 47kt) and wind waves of 9.5 m. These conditions compared well to the conditions forecast by WAVEWATCH III for that hour and position.

WAVEWATCH III model forecast for 15 UTC 24 November 2013 with position of Polarstern marked

In the period between the intermediate and main SYNOP reports, from 15 to 18 UTC on 24 November, there was a marked change in conditions. This leads us to speculate that this was when the vessel moved through the surface cold front. The observations that support this conclusion include the following.

  • The pressure began to increase, and continued to do so significantly well into 24 November. Before then, the pressure had shown a steady decreasing trend.
  • The wind intensity decreased from 46 to 42kt.
  • The wind direction changed to westerly, as would be expected after crossing through a frontal region.
  • While there was no precipitation at the 15 and 18 UTC synoptic observation times on 24 November, the past weather reported for both SYNOP messages reveal broken to overcast cloud conditions over the period, as well as showers in the hour preceding both synoptic observations. Such showers are expected mainly while passing through the cold front.