Rammasun makes landfall in southern China

July 18th, 2014

COMS-1 10.8 µm infrared channel images [click to play animation]

COMS-1 10.8 µm infrared channel images [click to play animation]

Super Typhoon Rammasun has made landfall in southern China – apparently this was the strongest typhoon to hit the South China region in 41 years (news story). The COMS-1 IR animation, above, shows the storm skirting along the north shore of the island of Hainan before hitting the south shore of the Leizhou Peninsula. A plot of the CIMSS Advanced Dvorak Technique indicated that Rammasun went though a period of rapid intensification on 17 July before reaching Super Typhoon intensity around 00 UTC on 18 July. The projected path (from this site) of the storm has it moving across the Gulf of Tonkin (where very warm Sea Surface Temperatures are present) and making landfall near the Vietnam/China border.

Past and Projected path of Rammasun, with Sea Surface Temperatures [click to enlarge]

Past and Projected path of Rammasun, with Sea Surface Temperatures [click to enlarge]

Visible imagery (below) captured the eye as it approached Hainan and then moved into the Qiongzhou strait between the island and the mainland. Note the initially mostly clear eye (with embedded small-scale vortices) rapidly fills after landfall.

COMS-1 0.675 µm infrared channel images [click to play animation]

COMS-1 0.675 µm infrared channel images [click to play animation]

A DMSP SSMIS 85 GHz microwave image (below) showed a well-defined eyewall at 1016 UTC.

DMSP SSMIS 85 GHz microwave image

DMSP SSMIS 85 GHz microwave image

A comparison of Suomi NPP VIIRS 11.45 µm IR and 0.7 µm “visible image at night” Day/Night Band data at 1735 UTC on 17 July (below; courtesy of William Straka, SSEC) revealed an interesting packet of waves in the southeastern quadrant of the eyewall region of the tropical cyclone.

Suomi NPP VIIRS 11.45 µm IR and 0.7 µm Day/Night Band images

Suomi NPP VIIRS 11.45 µm IR and 0.7 µm Day/Night Band images

Typhoon Neoguri threatens Okinawa

July 7th, 2014
COMS-1 0.675 µm and MTSAT-2 0.73 µm Visible channel images (Click to enlarge)

COMS-1 0.675 µm and MTSAT-2 0.73 µm Visible channel images (Click to enlarge)

Typhoon Neoguri is forecast to move west of Okinawa later today. The visible images above, from COMS-1 (left) and MTSAT-2 (right) show the storm at around 0800 UTC on 7 July 2014. A distinct eye filled with low-level clouds is apparent.

COMS-1 (left) and MTSAT-2 (right) visible channel images [click to play animation]

COMS-1 (left) and MTSAT-2 (right) visible channel images [click to play animation]

Magnified views of the storm center (above; click image to play animation; also available as an MP4 movie file) revealed the presence of mesovortices within the eye of Neoguri. The more frequent imaging schedule of COMS-1 (generally every 15 minutes, compared to every 30 minutes with MTSAT-2) allowed the cyclonic circulation of the mesovortices to be more easily identified. Another curious feature seen on the early morning visible imagery was a northwest-to-southeast oriented “cloud cliff” shadow just north of the eye, which was cast by the taller clouds of an eyewall convective burst just to the east. This same signature was seen again on the following morning, in nearly the same location relative to the eye (MTSAT-2 visible/IR image comparison).

METOP-B ASCAT winds over Neoguri and Observed SSTs (Click to toggle)

METOP-B ASCAT winds over Neoguri and Observed SSTs (Click to toggle)

ASCAT winds from METOP-B (above) show the structure of the typhoon, with 70-knot winds indicated. The Sea Surface Temperature (SST) image (taken from the CIMSS Tropical Cyclones site) also shows the extreme warmth of the western Pacific Ocean.

COMS-1 10.8 µm and MTSAT-2 10.8 µm Infrared channel images (Click to animate)

COMS-1 10.8 µm and MTSAT-2 10.8 µm Infrared channel images (Click to animate)

Infrared imagery from the past 24 hours show a decline in the satellite structure of the storm. Cold cloud tops have eroded from the northern and western quadrants of the storm, and a circular ring of cold cloud tops around the eye is no longer apparent.

Suomi NPP VIIRS 11.45 µm  Infrared channel image (Click to enlarge)

Suomi NPP VIIRS 11.45 µm Infrared channel image (Click to enlarge)

Suomi NPP overflew the storm on Saturday 5 July at 1620 UTC. The color-enhanced VIIRS 11.45 IR image, above (courtesy William Straka, SSEC/CIMSS), shows very cold cloud tops (185 K) southeast of a developing eye.

Hurricane Arthur transitions to an extratropical cyclone

July 6th, 2014
GOES-13 6.5 µm water vapor channel images with surface pressure and frontal analyses

GOES-13 6.5 µm water vapor channel images with surface pressure and frontal analyses

GOES-13 6.5 µm water vapor channel images with overlays of surface pressure and frontal analyses (above) showed Category 2 Hurricane Arthur (NHC discusions | blog post) transitioning to a powerful extratropical (or “post-tropical”) storm as it moved northward over the Maritime Provinces of Canada on 05 July 2014. Impacts of Hurricane Arthur along the East Coast of the US included a peak wind gust of 101 mph at Cape Lookout, North Carolina, and over 6 inches of rainfall in eastern Maine.

A long animation of 4-km resolution GOES-13 6.5 µm water vapor channel images covering the period 00:15 UTC on 05 July to 12:15 UTC on 06 July (below; click image to play animation; also available as an MP4 movie file) showed a very pronounced area of dry air (bright yellow to red color enhancement) wrapping into the circulation of the storm. Also evident on the water vapor imagery was the subsequent development of a “sting jet” signature along the southwestern and southern flank of the storm — this feature was associated with very strong winds (peak gust of 138 km/h or 86 mph) being transported down to the surface over parts of Nova Scotia and New Brunswick (Canadian Hurricane Centre statement). The sting jet signature resembles a “scorpion tail” (22:45 UTC image); note that there is a significant parallax offset with the >50 degree satellite viewing angle of GOES-13 imagery over this region, so the sting jet signature was actually located farther to the south over Nova Scotia (where the strongest surface winds were observed). Other notable sting jet cases appear here, here and here.

GOES-13 6.5 µm water vapor channel images (click to play animation)

GOES-13 6.5 µm water vapor channel images (click to play animation)

As an aside, it is interesting to examine the effect that the northeastward passage of Hurricane Arthur had on the pattern of sea surface temperatures in the far western Atlantic Ocean off the East Coast of the US. The Suomi NPP VIIRS Sea Surface Temperature (SST) product at 17:27 UTC on 05 July (below) revealed a number of filaments and eddies along the path of the tropical cyclone. A comparison with the 00 UTC 05 July Real-Time Global Sea Surface Temperature High-Resolution (RTG_SST_HR) analysis showed that even a 1/12 degree resolution model had difficulty resolving many of these subtle SST features — this helps to underscore the value of high-spatial resolution satellite imagery for making highly-accurate assessments of such fields as SST.

Suomi NPP VIIRS Sea Surface Temperature product, with a comparison to the RTG_SST_HR analysis

Suomi NPP VIIRS Sea Surface Temperature product, with a comparison to the RTG_SST_HR analysis

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).