Super Typhoon Usagi

September 19th, 2013 |
MTSAT-2 10.8 µm IR images (click image to play animation)

MTSAT-2 10.8 µm IR images (click image to play animation)

McIDAS images of MTSAT-2 10.8 µm IR channel data (above; click image to play animation) showed Super Typhoon Usagi in the West Pacific Ocean as it continued to move northwestward across the Philippine Sea. Note the slight amount of “trochoidal wobble” seen in the path of the eye. The coldest IR brightness temperature seen on the MTSAT-2 IR images was -92º C at 12:32 UTC. At the time of these images, advisories issued by the Joint Typhoon Warning Center listed the maximum sustained winds at 140 knots, with gusts to 170 knots; at its peak intensity, Usagi had an estimated lowest pressure of 882 hPa, making it the most intense tropical cyclone so far in 2013.

TMI and SSM/I 85 GHz microwave brightness temperature images

TMI and SSM/I 85 GHz microwave brightness temperature images

From the CIMSS Tropical Cyclones site, a comparison of 85 GHz microwave images from the TRIMM Microwave Imager (TMI) at 10:35 UTC and the DMSP SSM/I at 19:13 UTC (above) displayed a very small ring of high brightness temperatures surrounding the “pinhole eye”.

MIMIC-TC morphed microwave images (below; click image to play animation) showed a well-defined closed eyewall during much of the early part of the day on 19 September.

MIMIC-TC morphed microwave imagery (click image to play animation)

MIMIC-TC morphed microwave imagery (click image to play animation)

 

MTSAT-2 IR image with AASCAT scatterometer surface winds

MTSAT-2 IR image with AASCAT scatterometer surface winds

Scatterometer surface winds from the ASCAT instrument at 13:17 UTC  (above) and the OSCAT instrument at 15:10 UTC  (below) showed the large areal coverage of strong winds around the center of Usagi.

MTSAT-2 IR image with OSCAT scatterometer surface winds

MTSAT-2 IR image with OSCAT scatterometer surface winds

 ===== 20 September Update =====

MTSAT-2 0.67 µm visible channel images (click image to play animation)

MTSAT-2 0.67 µm visible channel images (click image to play animation)

MTSAT-2 0.67 µm visible channel images (above; click image to play animation) showed the detailed structure of the compact eye of Super Typhoon Usagi.

Hurricane Manuel near the west coast of Mexico

September 19th, 2013 |
Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band images

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

AWIPS images of Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm DayNight Band data showed Hurricane Manuel centered just off the west coast of Mexico at 07:54 UTC or 12:54 AM local time (above) and at 09:37 UTC or 2:27 AM local time (below) on 19 September 2013. Manuel had just reached hurricane intensity several hours earlier. In the 07:54 UTC images above, hints of an eye feature were present on both the IR and the Day/Night Band. In the 09:37 UTC images below, evidence of offshore convective bursts could be seen (many of which exhibited cloud-top IR brightness temperatures of -80º C and colder, violet color enhancement).

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

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

Manuel rapidly lost organization and intensity upon moving inland over the rugged terrain of the Sierra Madre Occidental, becoming a remnant area of low pressure over northern Mexico at the end of the day on 19 September.

Update on the Colorado flooding

September 17th, 2013 |
Before (07 September) and after (17 September) MODIS false-color Red/Green/Blue (RGB) images

Before (07 September) and after (17 September) MODIS false-color Red/Green/Blue (RGB) images

A comparison of “before” (07 September 2013) and “after” (17 September 2013) 250-meter resolution MODIS false-color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed a dramatic change in the appearance of the South Platte River that flows northeastward across northeastern Colorado. Following the record-setting rainfall across much of the Front Range of Colorado (previous blog post), much of this water (darker blue in appearance on the RGB images) was being carried across northeastern Colorado by the South Platte River and its tributaries.

Hydrographs for 3 different locations along the South Platte River in Colorado (Kersey, Balzac, and Julesburg, below) showed the actual and forecast maximum river crests — note that the peak river crest of 18.79 feet at Kersey eclipsed the previous record of 11.7 feet set in 1973.

A comparison of AWIPS images of consecutive overpasses (1 hour and 44 minutes apart) of Suomi NPP VIIRS 1.61 µm near-IR data on 14 September (below) appeared to indicate that the dark signal of the leading edge of the South Platte River flooding could be seen moving rapidly southeastward along that particular portion of the river.

The Suomi NPP VIIRS 1.61 µm image at 19:58 UTC on 17 September (below) showed that the dark signature of flooding along the South Platte River had nearly reached the Colorado/Nebraska border.

Note that the South Platte River flooding is not evident on the corresponding 0.64 µm VIIRS visible channel image (below) — this is due to the fact that there is not much contrast between the sediment-rich water and the adjacent dry soils (much of northeastern Colorado remains in a drought).

Suomi NPP VIIRS 0.64 µm visible channel and 1.61 µm near-IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 1.61 µm near-IR channel images

===== 18 September Update =====

Suomi NPP VIIRS 1.61 µm near-IR images (17 vs 18 September)

Suomi NPP VIIRS 1.61 µm near-IR images (17 vs 18 September)

A comparison of AWIPS images of Suomi NPP VIIRS 1.61 µm near-IR images (above) showed the progression of the leading edge of the flooding along the South Platte River in a 24-hour period (from 19:58 UTC on 17 September to 19:42 UTC on 18 September). The dark signal of river flooding had extended northeastward across the Nebraska border.

The hydrograph for Julesburg in far northeastern Colorado (below) showed that the river had already crested above the previous record stage of 10.4 feet.

Julesburg, Colorado hydrograph

Julesburg, Colorado hydrograph

Tropical Storm (formerly Hurricane) Humberto

September 16th, 2013 |
GOES-13 10.7 µm IR channel image (with track of Humberto)

GOES-13 10.7 µm IR channel image (with track of Humberto)

A GOES-13 10.7 µm IR channel image with the track of Humberto from the CIMSS Tropical Cyclones site  (above) showed that the storm (which became the first hurricane of the season in the Atlantic Basin on 11 September) had been meandering over the eastern North Atlantic Ocean for several days, eventually weakening to a post-tropical cyclone on 14 September before re-organizing into a tropical storm early in the day on 16 September (NHC advisories archive).

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

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

A GOES-13 0.63 µm visible channel image with an overlay of ASCAT surface scatterometer winds (above) showed evidence of tropical storm force winds (yellow wind barbs) north of the storm center at 13:17 UTC. Note the presence of a well-defined cloud vortex located southwest of the 18 UTC center fix position.The NHC discussion #26 mentioned that several smaller-scale vortices had been rotating around the mean circulation center of Humberto — and a close-up view using GOES-13 0.63 µm visible channel images (below; click image to play animation) revealed one of these exposed vortices to the southwest of the center of Humberto.

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

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

See From the Lee Side for a discussion on the role of vertical wind shear on tropical cyclones such as this.