The effect of wind shear on Tropical Storm Karina

August 24th, 2014
GOES-15 0.63 µm visible channel  images (click to play Animated GIF)

GOES-15 0.63 µm visible channel images (click to play Animated GIF)

GOES-15 0.63 µm visible channel images (Animated GIF | MP4 movie | YouTube video | QuickTime movie) showed the decoupling of the upper-level and lower-level circulations of Tropical Storm Karina in the East Pacific Ocean on 24 August 2014. This decoupling was caused by strong wind shear along the western periphery of Category 5 Hurricane Marie, which was located to the east-southeast of Karina (large-scale view). Kudos to Dennis Chesters (NASA/Goddard) for bringing this interesting case to our attention (and providing the QuickTime movie linked to above).

The corresponding GOES-15 10.7 µm IR channel images (Animated GIF | MP4 movie | YouTube video) showed the cold clouds (red to black to white to purple color enhancement) associated with the upper-level circulation moving northward and quickly dissipating; the signature of the warmer clouds (darker cyan color enhancement) associated with the lower-level circulation can also be seen emerging from beneath the cold cloud shield and moving eastward.

GOES-15 10.7 µm IR channel images (click to play Animated GIF)

GOES-15 10.7 µm IR channel images (click to play Animated GIF)

A closer view provided by a Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image from the SSEC RealEarth web map server (below) showed the separation of the upper-level and lower-level circulations around 21:53 UTC.

Suomi NPP VIIRS true-color RGB image

Suomi NPP VIIRS true-color RGB image

A sequence of 4 images (15, 18, 21, and 00 UTC) from the CIMSS Tropical Cyclones site (below) shows GOES-15 6.5 µm water vapor channel images with overlays of deep-layer wind shear (derived from satellite winds). To the east of Karina (which was located in the center of the images), the large anticylcone aloft associated with Category 5 Hurricane Marie can be seen, with increasing vales of southeasterly wind shear moving over Karina.

GOES-15 6.5 µm water vapor images with overlays of deep layer wind shear

15 UTC GOES-15 6.5 µm water vapor images with overlays of deep layer wind shear

The 3 image comparisons below show the separation of the centers of upper-level divergence (yellow) and lower-level convergence (cyan) as the decoupling process was occurring at 18 UTC, 21 UTC, and 00 UTC.

18 UTC GOES-15 6.5 µm water vapor image with upper-level divergence (yellow) and GOES-15 10.7 µm IR image with lower-level convergence (cyan)

18 UTC: GOES-15 6.5 µm water vapor image with upper-level divergence (yellow) and GOES-15 10.7 µm IR image with lower-level convergence (cyan)

21 UTC: GOES-15 6.5 µm water vapor image with upper-level divergence (yellow) and GOES-15 10.7 µm IR image with lower-level convergence (cyan)

21 UTC: GOES-15 6.5 µm water vapor image with upper-level divergence (yellow) and GOES-15 10.7 µm IR image with lower-level convergence (cyan)

00 UTC: GOES-15 6.5 µm water vapor image with upper-level divergence (yellow) and GOES-15 10.7 µm IR image with lower-level convergence (cyan)

00 UTC: GOES-15 6.5 µm water vapor image with upper-level divergence (yellow) and GOES-15 10.7 µm IR image with lower-level convergence (cyan)

===== 25 August Update =====

GOES-15 0.63 µm visible channel images, with Metop ASCAT surface scatterometer winds

GOES-15 0.63 µm visible channel images, with Metop ASCAT surface scatterometer winds

Even though the southeastward-moving low-level circulation of Karina had been downgraded to a Tropical Depression with 30 knot winds, there was still an impressive burst of convection just west of the center as it began to move back over warmer water on 25 August. Metop ASCAT surface scatterometer winds (above) showed a small pocket of winds in the 30.0-39.9 knot range (green wind barbs) at 18:29 UTC.

There were also some Tropical Overshooting Top (TOT) targets detected within the convective burst (below); TOT symbols: Red = 0-1 hour previous, Green = 1-2 hours previous, Blue = 2-3 hours previous.

GOES-15 Infrared - Water Vapor difference product, and Tropical Overshooting Tops product (TOT symbols: Red = 0-1 hour previous, Green = 1-2 hours previous, Blue = 2-3 hours previous)

GOES-15 Infrared – Water Vapor difference product, and Tropical Overshooting Tops product (TOT symbols: Red = 0-1 hour previous, Green = 1-2 hours previous, Blue = 2-3 hours previous)

Mesovortices within the eye of Hurricane Lowell

August 21st, 2014
GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (above; click image to play animation; also available as an MP4 movie file) revealed the presence of mesovortices within the eye of Category 1 Hurricane Lowell in the East Pacific Ocean on 21 August 2014.

The mesovortices were also evident at 21:07 UTC in a Suomi NPP VIIRS true-color image from the SSEC RealEarth web map server (below).

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image

In addition to having a rather large eye, Hurricane Lowell also had a large radius of strong winds, as seen on a comparison of a GOES-15 0.63 µm visible image and Metop ASCAT surface scatterometer winds from the CIMSS Tropical Cyclones site (below).

GOES-15 0.63 µm visible channel image with Metop ASCAT surface scatterometer winds

GOES-15 0.63 µm visible channel image with Metop ASCAT surface scatterometer winds

Long-range transport of Canadian wildfire smoke

July 8th, 2014

GOES-15 (top) and GOES-13 (bottom) 0.63 µm visible channel images [click to play animation]

GOES-15 (top) and GOES-13 (bottom) 0.63 µm visible channel images [click to play animation]

On 08 July 2014 a comparison of GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel images (above; click image to play animation; also available as an MP4 movie file) showed the southward and southeastward transport of dense smoke from wildfires that were burning in the Northwestern Territories of Canada. Over the Lower 48 states, the leading edge of the smoke made it as far south as Iowa and northern Illinois. The bulk of the dense smoke was aloft, but at the surface the visibility was reduced to 3-5 miles at some locations in North Dakota.

The above example serves as a good demonstration of the principle of “forward scattering”: the smoke was more evident on visible imagery from GOES-15  early in the day (as the sun was rising), and more evident on visible imagery from GOES-13 later in the day (as the sun was setting).

Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from the SSEC RealEarth web map server (below) showed the areal coverage of the hazy pall of smoke on 06 July, 07 July, and 08 July.

Suomi NPP VIIRS true-color images

Suomi NPP VIIRS true-color images

The IDEA-I forward airmass trajectory model applied to targets of high Aerosol Optical Depth (AOD) which were detected by the Terra MODIS instrument over Canada on 08 July are shown below. Such a tool can be used as an aid in air quality forecasting.

IDEA-I MODIS Aerosol Optical Depth and forward trajectories (click to play animation)

IDEA-I MODIS Aerosol Optical Depth and forward trajectories (click to play animation)

===== 09 July Update =====

The Terra MODIS AOD product (below; click to play animation) indicated that the leading edge of the Canadian wildfire smoke had advanced as far southward as northwestern Missouri. The bulk of the highest AOD values over the Dakotas was forecast to be transported slowly east-northeastward toward the Great Lakes region.

IDEA-I MODIS Aerosol Optical Depth and forward trajectories (click to play animation)

IDEA-I MODIS Aerosol Optical Depth and forward trajectories (click to play animation)

Hurricane Arthur

July 3rd, 2014
Terra MODIS 11.0 µm IR channel image

Terra MODIS 11.0 µm IR channel image

04 July Update: a 1-km resolution Terra MODIS 11.0 µm IR image (above) showed the eye of Category 2 Hurricane Arthur making landfall along the coast of North Carolina around 03:13 UTC or 11:15 pm Eastern Time. Arthur was the earliest hurricane to make landfall in North Carolina since records began in 1851 (the previous record was 11 July, 1901).

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

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

[5:45 PM EDT 3 July 2014 Update: The animation of GOES-13 visible images above, ending at 21:45 UTC or 5:45 PM Eastern Daylight Time, shows Hurricane Arthur very close to the North Carolina coast. Convection continues redeveloping in the circulation close to the eye.]

Suomi NPP VIIRS True Color Image of Arthur at 1800 UTC 3 July 2014

Suomi NPP VIIRS True Color Image of Arthur at 1800 UTC 3 July 2014

The original VIIRS image, above (courtesy of Russ Dengel), was clipped from this link. An animation of VIIRS True-Color imagery of Arthur (courtesy of Kathy Strabala), taken from the Webmap server at SSEC is shown below.

Suomi NPP VIIRS True Color Imagery of Arthur, 30 June - 3 July 2014 (click to enlarge)

Suomi NPP True Color Imagery of Arthur, 30 June – 3 July 2014 (click to enlarge)

GOES-13 10.7 µm infrared channel images (click to play animation)

GOES-13 10.7 µm infrared channel images (click to play animation)

Tropical Storm Arthur has strengthened overnight to become the first hurricane of the Atlantic Tropical Season. The storm-centered animation above, from GOES-East, (click here for an animation without the map) shows evidence of the relaxation in wind shear that has allowed intensification. At the beginning of the animation, most convection is to the east and south of the system. By 3 July, convection is much closer to the center of the strengthening storm and an outflow channel to the southeast has developed; a distinct eye is present by 2045 UTC on 3 July. Note that in the color enhancement that the coldest cloud tops — purple — are cooler than -80° C. This image (from this website) shows Arthur, at 1500 UTC on 3 July 2014, under a minimum in wind shear. (Zoomed-in version of wind shear).

The tropical cyclone has been moving due north over the past 24 hours, but the National Hurricane Center notes that a recurvature to the northeast is occurring now. Interests along the South and North Carolina coasts should pay special attention to forecasts for today and tomorrow.

GOES-13 0.63 µm visible channel image with surface observations, 1400 UTC 3 July 2014 (click to enlarge)

GOES-13 0.63 µm visible channel image with surface observations, 1400 UTC 3 July 2014 (click to enlarge)

Visible imagery from 1400 UTC, above, does not yet show an eye, and strongest winds at that time remained offshore. Moored Buoy 41004 (41 miles southeast of Charleston, SC, at 32°30’2″ N 79°5’58″ W) shows tropical-storm force-winds; a plot of the pressure and winds at the station, below, suggests an approaching storm.

Surface Pressure and Winds at Moored Buoy 41004 (click to enlarge)

Surface Pressure and Winds at Moored Buoy 41004 (click to enlarge)

Toggle between Suomi NPP VIIRS 11.45µm Infrared Imagery and Day/Night Band at 0639 UTC 3 July (click to enlarge)

Toggle between Suomi NPP VIIRS 11.45µm Infrared Imagery and Day/Night Band at 0639 UTC 3 July (click to enlarge)

Suomi NPP overflew Arthur in the early morning of July 3rd, affording a high-resolution view of the convective clouds. The coldest overshooting tops, around -85°C are far to the east of the surface circulation, but a large cirrus shield with temperatures near -75°C is over the storm center. The Day/Night band shows little contrast because the Quarter Moon set at 0400 UTC and therefore no lunar illumination is available. A few lightning streaks in the convection around Arthur are present. Lightning is far more common in the convection over the northeast Gulf of Mexico.

MODIS Imagery over Arthur at 1613 UTC 3 July (click to cycle through channels)

MODIS Imagery over Arthur at 1613 UTC 3 July (click to cycle through channels)

MODIS imagery over Arthur was available from Terra at 1613 UTC today. A variety of channels are shown above — Visible imagery (0.64 µm), the Snow/Ice Channel (a wavelength of 1.6 µm, at which snow/ice strongly absorb radiation and therefore appear dark), the Cirrus channel (a wavelength of 1.38 µm, at which cirrus clouds are strongly reflective and are therefore highlighted), the Water Vapor channel (6.7 µm, showing the height of the top of the moist layer) and the Infrared channel near 11 µm.

Previous Tropical Storm Arthurs passed near the North Carolina coast in 1996 (a swirl in mid-level clouds with little deep convection) and in 2002 (a mass of convection that obscured any circulation).