Hurricane Gonzalo moves towards Bermuda

October 16th, 2014
GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

Small and intense Hurricane Gonzalo is moving north-northeastward out of the western tropical Atlantic towards Bermuda (Bermuda is located at 32.3º N, 64.8º W). (See the National Hurricane Center Website for the latest Advisories on Gonzalo) GOES-13 Visible imagery (0.63 µm) from the morning of 16 October shows a well-defined eye, intense convection and good outflow in all quadrants. Mesovortices within the eye are also apparent as shown in a storm-centered animation of the eye, below, until mid- and high-level clouds develop near the end of the animation.

GOES-13 0.63 µm visible channel images, centered over the eye of Gonzalo (click to play animation)

GOES-13 0.63 µm visible channel images, centered over the eye of Gonzalo (click to play animation)

Gonzalo’s track will take it over sea surface temperatures that are not quite so warm (see image below, taken from the CIMSS Tropical Cyclones site). Cooler SSTs argue against any further strengthening, and the official forecast suggests peak intensity has already occurred.

Sea Surface Temperatures and Gonzalo's projected (and past) track and intensity (click to enlarge)

Sea Surface Temperatures and Gonzalo’s projected (and past) track and intensity (click to enlarge)

Suomi NPP overflew the storm at 0536 UTC in 16 October. A toggle between the VIIRS Day/Night Band and the 11.45 µm imagery is below. Note that lunar illumination is dropping as the Moon phase wanes so visible features are less distinct than they would be during a more Full Moon. A ragged eye is obvious in both images, however, and there is evidence of a lightning streak well east of the eye in the Day/Night Band.

Suomi NPP Day/Night Band Visible Imagery and 11.45 µm Infrared Imagery (click to enlarge)

Suomi NPP Day/Night Band Visible Imagery and 11.45 µm Infrared Imagery (click to enlarge)

Both Aqua and Metop-A overflew Gonzalo during the day on 16 October. The Aqua True-Color image (from the MODIS Today website) shows the storm and the cold front that will help guide Gonzalo’s future path. The ASCAT scatterometer data from METOP-A, below, showed a tight region of hurricane-force winds.

METOP-A ASCAT Scatterometer winds, 1353 UTC 16 October 2014 (click to enlarge)

METOP-A ASCAT Scatterometer winds, 1353 UTC 16 October 2014 (click to enlarge)

===== 18 October Update =====

Suomi NPP VIIRS 11.45 µm IR channel images

Suomi NPP VIIRS 11.45 µm IR channel images

A sequence of Suomi NPP VIIRS 11.45 µm IR channel images during the 15-17 October period (above) showed the pattern of very cold cloud-top IR brightness temperatures at various times as the storm curved northward toward Bermuda (station identifier TXKF); IR brightness temperatures of -80º C and colder (violet color enhancement) were seen on 15 and 16 October. A close-up view shows Gonzalo on 2 consecutive VIIRS IR images (16:38 and 18:18 UTC) on 17 October.

The MIMIC Total Precipitable Water (TPW) product (below; click image to play animation) showed a plume of high TPW ahead of a cold front moving off the East Coast of the US, which was then reinforced by a northward surge of high TPW from Ganzalo. As a result, the TPW value calculated using the morning rawinsonde data from Caribou, Maine (station identifier KCAR) was 1.68 inches — the highest for so late in the season.

MIMIC Total Precipital Water product (click to play animation)

MIMIC Total Precipital Water product (click to play animation)

Around 20:15 UTC on 17 October, a comparison of GOES-13 10.7 µm IR channel and SSMIS 85 GHz microwave images from the CIMSS Tropical Cyclones site (below), the microwave image revealed the very large size of the eye of Hurricane Gonzalo (which was not as apparent on conventional IR imagery).

GOES-13 10.7 µ IR image and SSMIS 85 GHz microwave image

GOES-13 10.7 µ IR image and SSMIS 85 GHz microwave image

A close-up view of GOES-13 10.7 µm IR channel images with overlays of wind barbs and wind gusts from Bermuda International Airport (below; click image to play animation) showed the development of a convective burst just as the eye of Gonzalo was approaching the island. The airport observations (text listing | time series plot) showed a wind gust to 83 knots (96 mph) as the northern eyewall passed, and a stronger gust to 98 knots (113 mph) as the southern eyewall passed over Bermuda.

GOES-13 10.7 µm IR channel images, with overlays of wind barbs and wind gusts at Bermuda (click to play animation)

GOES-13 10.7 µm IR channel images, with overlays of wind barbs and wind gusts at Bermuda (click to play animation)

The Bermuda Weather Service launched a rawinsonde balloon at 00 UTC on 18 October; winds at the surface were from the southeast at 64 knots (74 mph), which carried the instrument package into the eye of Gonzalo for a portion of its ascent. Note the the temperature profile was nearly moist adiabatic from about 700 hPa to 200 hPa (below).

Bermuda rawinsonde report and GOES-13 10.7 µm IR image

Bermuda rawinsonde report and GOES-13 10.7 µm IR image

Tropical Invest 97L in the western Atlantic Ocean

September 29th, 2014
GOES-13 0.63 µm visible channel images with METAR surface reports (click to play animation)

GOES-13 0.63 µm visible channel images with METAR surface reports (click to play animation)

Tropical Invest 97L formed near Bermuda during the pre-dawn hours on 29 September 2014. After sunrise, AWIPS II images of GOES-13 0.63 µm visible channel data (above; click image to play animation) revealed a well-defined low-level circulation spinning just to the west of Bermuda. It is interesting to note that at 12:55 UTC a waterspout was reported 4 km to the east of the Bermuda International Airport (station identifier TXKF), associated with a band of deep convection that was moving northward (below).

GOES-13 0.63 µm visible channel image with Bermuda METAR observation

GOES-13 0.63 µm visible channel image with Bermuda METAR observation

An overpass of a Metop satellite at 14:38 UTC provided a good view of the surface wind field with data from the ASCAT scatterometer instrument (below). There was one wind vector with a speed around 30 knots (green) just to the east of the center of circulation.

GOES-13 0.63 µm visible channel image with Metop ASCAT scatterometer surface winds

GOES-13 0.63 µm visible channel image with Metop ASCAT scatterometer surface winds

A comparison of Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images at 15:25 UTC (below) showed that the coldest cloud-top IR brightness temperatures of -55º C (orange color enhancement) were located to the north of the circulation center.

Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images

Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images

Strong early-season storm in the North Pacific

September 23rd, 2014
GOES-15 6.5 µm IR channel images (click to play animation)

GOES-15 6.5 µm IR channel images (click to play animation)

The GOES-15 6.5 µm water vapor channel imagery above showed the development and evolution of a strong mid-latitude cyclone in the eastern North Pacific Basin during the 21-23 September 2014 time period; of particular interest was the development of strong subsidence behind the storm (depicted by brighter shades of yellow), and also a second jet starting to approach the storm from the west (as evidenced by increasing cold cloud tops in the base of the trough at the end of the animation). A closer view of the storm using AWIPS II imagery is available here. The strong storm had access to abundant sub-tropical moisture, as depicted in the MIMIC Total Precipitable Water animation below.

MIMIC Total Precipitable Water (click to enlarge)

MIMIC Total Precipitable Water (click to enlarge)

The ASCAT Scatterometer that flies on METOP gives routine observations of surface winds over the ocean. A large area of storm-force winds (in red) was depicted in the image below (from 0630 UTC on 23 September), overlain on the GOES-15 Water Vapor imagery.

 GOES-15 6.5 µm water vapor channel image and ASCAT winds, 0630 UTC on 23 September (click to enlarge)

GOES-15 6.5 µm water vapor channel image and ASCAT winds, 0630 UTC on 23 September (click to enlarge)

A comparison of 4-km resolution GOES-15 6.5 µm and 1-km resolution Aqua MODIS 6.7 µm water vapor channel images at 11:30 UTC, below, demonstrated the benefit of higher spatial resolution for providing a more accurate display of the water vapor gradients and various small-scale features (such as transverse banding associated with cold clouds to the north of the storm), along with the polar-orbiter image elimination of geostationary parallax error for more more precise feature location.

GOES-15 6.5 µm and Aqua MODIS 6.7 µm water vapor channel images

GOES-15 6.5 µm and Aqua MODIS 6.7 µm water vapor channel images

The GOES sounder Total Column Ozone product, below, showed an increase in ozone values (350-380 Dobson Units, darker green to lighter green color enhancement) as the tropopause was lowered in the vicinity of the deepening mid-latitude cyclone.

GOES sounder Total Column Ozone product (click to play animation)

GOES sounder Total Column Ozone product (click to play animation)

A Suomi NPP VIIRS true-color image from the SSEC RealEarth web map server, below, provided a good view of the lower-level clouds associated with the storm.

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image

For a more detailed analysis of this event from the Ocean Prediction Center perspective, see the Satellite Liaison Blog.

Tropical Storm Dolly in the southern Gulf of Mexico

September 2nd, 2014
Suomi NPP VIIRS Day Night Band (0.70 µm) image (click to enlarge)

Suomi NPP VIIRS Day Night Band (0.70 µm) image (click to enlarge)

Tropical Storm Dolly has formed in the western Gulf of Mexico. The Suomi NPP VIIRS Day Night Band imagery, above, shows the exposed low-level swirl of the storm (then still a tropical depression). North-northwesterly shear (shown here, from this site) means the deep convection (shown below) is displaced to the east of south of the the low-level circulation (click here for a toggle between the Day Night Band and the 11.45µm imagery). Cloud-top IR brightness temperatures from VIIRS were as cold as -87º C. ASCAT winds from 0230 UTC show a region of tropical storm-force winds associated with convection east and north of the circulation center.

Suomi NPP VIIRS Infrared (11.45 µm) image (click to enlarge)

Suomi NPP VIIRS Infrared (11.45 µm) image (click to enlarge)

Early-morning visible imagery from GOES-13, below, shows the large area of convection over the southern Gulf. The NHC-reported positions of the storm at 0900 UTC and 1500 UTC (22.6º N, 94.8º W and 23.4º N, 96.5º, respectively) are indicated by the red boxes on the images. Strong convection just south of the surface circulation developed at sunrise, obscuring the low-level swirl. That strong convection is especially apparent in the GOES-13 10.7 imagery, at bottom. GOES IR Brightness Temperatures were as cold as -84º C in the animation. (For more on Dolly from the National Hurricane Center, see this link).

GOES-13 Visible Imagery (0.63 µm) (click to animate)

GOES-13 Visible Imagery (0.63 µm) (click to animate)

GOES-13 Infrared Imagery (10.7 µm) (click to animate)

GOES-13 Infrared Imagery (10.7 µm) (click to animate)