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Archive for the ‘WindSat’ Category

Strong winds have been occurring for the last several days in the Gulf of Tehuantepec of the eastern Pacific Ocean, to the south of eastern Mexico.  These strong gap winds result from cool high pressure systems that surge southward through the western Gulf of Mexico, with the air funneled through the relatively lower elevation of Chivela Pass in eastern Mexico (Fig. 1).  These high winds have been nicely depicted by the Weather Research and Forecasting (WRF) model runs produced through a collaboration between SPoRT and NASA/SERVIR, as shown by the 30-h forecast maximum hourly 10-m wind speed in Fig. 2, valid on 1200 UTC 12 November.  A corresponding image of WindSat retrieved winds is shown in Fig. 3 for roughly the same time as the WRF model forecast.

The SPoRT/SERVIR WRF model forecasts over the Caribbean and Central America are unique in that the model runs are generated daily in real-time using cloud computing resources.  The model runs are initialized at 0600 UTC, ingest SPoRT sea surface temperatures in the initial conditions, and are integrated out to 48 hours.  The team is working to migrate the model output to a real-time web map service.

This latest surge of cold air impacting the U.S. Deep South today will continue unabated into the Gulf of Tehuantepec over the next day or so.  Today’s SPoRT/SERVIR WRF model run suggests a substantial increase in the wind speeds to over 20 m/s by 0600 UTC 14 November (Fig. 4).  Winds are forecast to exceed 20 m/s from about 1500 UTC 13 November through 1200 UTC 14 November.   The National Hurricane Center’s Tropical Analysis and Forecast Branch put out an experimental graphic indicating this expected increase in wind speeds and accompanying high seas in the eastern Pacific Ocean (Fig. 5).

Figure 1.  Topography in Eastern Mexico leading to strong gap winds in the Gulf of Tehuantepec.

Figure 1. Topography in Eastern Mexico leading to strong gap winds in the Gulf of Tehuantepec.
Image credit: http://www.wunderground.com/blog/24hourprof/tehuantepecer.

Figure 2.  Thirty-hour forecast of maximum hourly 10-m wind speed (m/s) from SPoRT/SERVIR WRF model run, valid at 1200 UTC 12 November 2013.

Figure 2. Thirty-hour forecast of maximum hourly 10-m wind speed (m/s) from SPoRT/SERVIR WRF model run, valid at 1200 UTC 12 November 2013.

Figure 3.  WindSat image of wind vector valid 1200 UTC 12 November 2013, courtesy of the Naval Research Laboratory.

Figure 3.  Image of retrieved WindSat winds valid 1225 UTC 12 November 2013, courtesy of the Naval Research Laboratory.

Figure 4.  Twenty-four hour forecast of maximum hourly 10-m wind speeds from the SPoRT/SERVIR WRF model, valid 0600 UTC 14 November 2013.

Figure 4. Twenty-four hour forecast of maximum hourly 10-m wind speeds from the SPoRT/SERVIR WRF model, valid 0600 UTC 14 November 2013.

Fig. 5.  Experimental Graphical Forecast produced by NHC's Tropical Analysis and Forecast Branch, valid through 0000 UTC 14 November 2013.

Fig. 5. Experimental Graphical Forecast produced by NHC’s Tropical Analysis and Forecast Branch, valid through 0000 UTC 14 November 2013.

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Given the very cold and snowy winter in Alaska this year, it is no doubt that surface observation systems are taking a beating, especially those out in the open ocean.   The loss of some of these important data makes operational forecasting a little more difficult.  Because of this, the use and importance of remotely sensed data has increased this winter.  In fact, Edward Liske, General Forecaster at the Juneau NWS office, has stated that they have been “depending a bit more on the satellite derived wind data that we get this winter for our marine forecasts because our surface marine observations are getting beaten to a pulp”.  He goes on to write,

“of the four offshore buoys in the eastern Gulf, one is dead, and two have broken wind sensors.  Our main inside channel obs are not much better, Cape Spencer and Sisters Island are down from low battery power, Point Retreat is not reporting wind gusts, Point Bishop is also down and Lincoln Rock was taken out by a combination of hurricane force winds, a high tide, and high waves.  That only leaves 3 inside channel sites and an offshore buoy that are working ok.”

Edward was kind enough to include some images that showed this strong outflow event. Figure 1 shows WindSat radiometer winds along parts of the Alaska peninsula together with IR imagery and a few fixed bouys on the 12th Jan 2012 at 0400Z.  Figure 2 shows strong outflow winds in the panhandle on the 16th of January around 1530-1600Z.

Figure 1. WindSat Radiometer Winds with GOES West IR imagery and Fixed Buoys (orange) on 12th Jan 2012 0400Z.

Figure 2. WindSat Radiometer Winds together with GOES West IR imagery and Fixed Bouys (light blue) on 16th Jan 2012 ~1530-1600Z.

Edward continued, “this particular outflow event produced storm and gale force winds in most of our inner channel zones and strong winds in our usual outflow areas (Skagway, Taku Inlet, passes east of Yakutat, and Disenchantment Bay).  Air temperatures did drop into the single digits so freezing spray was a concern as well.”
This is clearly a great example of the operational benefit of remotely sensed observations when in-situ observations suffer degradation due to harsh conditions.

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Operational forecasting and monitoring weather conditions for marine environments can be particularly difficult, mainly due to the lack of observational networks.  This is why satellite observations can be so useful, especially when components of the already sparse network fail.  Sven Nelaimischkies, a forecaster at the Medford, OR NWS office, recently found some utility in the WindSat data provided by SPoRT, and was kind enough to share this information with us. The Medford office recently had a strong wind event on our coast, that came in two weakly separated shots on the 21st and 22nd. The first day saw storm force winds that knocked out the anemometers and damaged the uplink antenna on buoy 46015. Around 12 hours earlier a pass offshore indicated ~50kt winds ahead of the second front that confirmed that the current warning in place looked on track. Attached is the pass during the middle of the event which was very helpful as the wind data was not available from the buoy at that time.  Buoy 46050 had wave data knocked out shortly after this, but it has since returned, unlike buoy 46015.

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As contrasted with the October 31 WindSat case (posted here last week), wind is light out of the south as indicated in the first figure from WindSat. We only have one moving marine observation in the hour before the pass for comparison shown in the second figure. These images would have been overlaid but for the one hour difference.

[We’re hoping to show/document the usefulness of WindSat data in many different forecasting situations and geographic areas.  – Matt Smith]

WindSat pass at 15Z

Moving marine surface obs and Buoy reports for 14Z

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During the morning of October 31 we had a gale event over the coastal waters just off the Northern California Coast. This presented a good opportunity to evaluate the operational usefulness of the WindSat data. During late spring and summer, strong gale to near gale conditions develop within a few miles off shore over the Northern California and Southern Oregon waters. On most days the wind peaks during the late afternoon or evening hours. The core of the northwesterly low level jet that forms is usually just beyond the buoy locations and hence not well sampled by surface obs. Even though this case occurred during October it has many of the characteristics of the summer gale events. Note the core of the low level jet off Cape Mendocino in light green with 35kt wind barbs indicating gale winds. This is a warning condition for Marine concerns (Figure 1).  Note the area of  > 34Kt wind indicated by yellow wind barbs (Figure 2). We see in this case very good correlation with the WFO forecast. Also provided is the GFS 12Z initialization of the surface winds with buoy data overlaid for comparison. The Marine forecast valid for that time frame is also provided for operational context.

Figure 1 - The 15Z surface wind forecast grid issued by the Eureka WFO overnight.

Figure 2 – The WindSat data for the same time frame, 15Z in the morning.

 

Figure 3 – Surface winds from the GFS for 12Z.

PT ST GEORGE TO CAPE MENDOCINO 10 TO 60 NM-
310 AM PDT MON OCT 31 2011

…SMALL CRAFT ADVISORY IN EFFECT UNTIL 10 AM PDT THIS
MORNING…
…GALE WARNING IN EFFECT FROM 10 AM PDT THIS MORNING THROUGH
TUESDAY EVENING…

.TODAY…N WIND 15 TO 20 KT…RISING TO 20 TO 30 KT WITH GUSTS TO 45 KT. WIND WAVES 4 FT…BUILDING TO 8 TO 10 FT. NW SWELL 5 FT AT 9 SECONDS…BECOMING N 5 TO 7 FT AT 10 SECONDS. PATCHY FOG AND SLIGHT CHANCE OF RAIN BEFORE SUNRISE.
.TONIGHT…N WIND 30 TO 35 KT WITH GUSTS TO 45 KT. WIND WAVES 12 TO 13 FT. N SWELL 7 TO 8 FT AT 10 SECONDS…BUILDING TO 11 TO 12 FT AT 10 SECONDS AFTER MIDNIGHT.
.TUE…N WIND 25 TO 35 KT WITH GUSTS TO 45 KT. WIND WAVES 11 TO 13 FT. N SWELL 10 TO 12 FT AT 13 SECONDS.

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Winds around a powerful storm system currently affecting mainly the western portions of Alaska with hurricane force winds, high seas, and blizzard conditions have been detected well by the WindSat instrument over the last couple of days.  The low pressure system, which is crossing the Chukotsk peninsula in eastern Russia, has deepened to as low as 946mb, but shows some recent weakening.  Nevertheless, wind gusts along the western coast of Alaska have been measured in the 70-90 mph range according to the NWS office in Fairbanks, Alaska.  http://www.arh.noaa.gov/wmofcst.php?wmo=NOAK49PAFG&type=public

We at SPoRT have been watching this storm and the evolution of winds as displayed by the WindSat instrument over the last couple of days.  This first image (Image 1), with WindSat

Figure 1. WindSat 1940Z 8 Sep 2011

measurements valid at 1940Z indicates wind speeds around the area of low pressure as high as 65 knots, as indicated by the red arrows.  Note in the image that the WindSat measurements appear as the green/yellow/red colors (in order of increasing intensity), while land-based METARs are colored orange, and fixed buoys appear in Cyan.  A gust of 62 knots with a peak of 68 knots occurred at fixed buoy 46035 at 2000Z, giving further credence to the WindSat values.  A wind speed of 35 knots with a gust to 47 knots can be seen at Point Hope on Alaska’s northwest coast in good agreement with nearby WindSat observations.  Also note that the winds helped to indicate the center of low pressure.  Winds around 30 to 40 knots can also be seen in still ice-free areas of the Chukchi sea.

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Comparison of Windsat ocean surface vectors with GFS, NAM, and in situ observations for Chukchi Sea, AK on October 27, 2011.

John Lingass (WCM in Fairbanks asked us to post this for him) The GFS and NAM output for this time frame of WindSat observation look very close to the WindSat observations, especially for the higher wind speeds. Although ship observations were not available, which would be the ultimate data for validation, the surface observations at Gambell (PAGM) and Savoonga (PASA) on St. Lawrence Island have some utility for comparison as the wind flow is coming from an unobstructed direction with regard to the wind instruments at these locations. The WindSat Data shows very good agreement with these land observations in this case. As for synoptic features, a 991 mb low was stationary and slowly weakening near the Bering Strait, the wind circulation excellently indicated by the WindSat data.

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