Tropical Storm Erika approaches the eastern Caribbean

August 26th, 2015

GOES-13 10.7 µm IR images [click to play animated GIF]

GOES-13 10.7 µm IR images [click to play animated GIF]

GOES-13 Infrared Imagery (above) for the 24 hours ending 1415 UTC on 26 August 2015 show Tropical Storm Erika approaching the Leeward Islands of the eastern Caribbean. A general increase in convection in the 24 hours shown is obvious. Visible imagery (below) from the morning of 26 August shows some overshooting tops within the central dense overcast (CDO) covering the low-level circulation. A plot of the number of overshooting tops in Erika is here (taken from this webpage). Outward-propagating gravity waves can also be seen at the top of the CDO.

GOES-13 Visible Imagery (0.63 µm) [click to play animated GIF]

GOES-13 Visible Imagery (0.63 µm) [click to play animated GIF]

Surface winds as observed by the Metop ASCAT Scatterometer early on 26 August (0056 UTC), below, show a modest circulation with winds that are mostly below tropical storm force (Added: The 1411 UTC image, bottom, shows some tropical-storm force wind flags). Dry Saharan Air Layer air should not limit intensification of Erika, but wind shear just north and west of the storm is strong (SAL and Wind Shear imagery taken from the CIMSS Tropical Cyclones site).

ASCAT Winds and GOES-13 Water Vapor IR (6.5 µm) [click to enlarge]

ASCAT Winds and GOES-13 Water Vapor IR (6.5 µm), ~0100 UTC 26 August 2015 [click to enlarge]

ASCAT Winds and GOES-13 Water Vapor IR (6.5 µm) [click to enlarge]

ASCAT Winds and GOES-13 Water Vapor IR (6.5 µm), ~1400 UTC 26 August 2015 [click to enlarge]

For the most recent forecasts on Erika’s future, see the National Hurricane Center website.

Twin Typhoons in the western Pacific

August 17th, 2015

Himawari-8 10.35 µm IR images [click to play animated GIF]

Himawari-8 10.35 µm IR images [click to play animated GIF]

Himawari-8 captured the trek of Typhoons Goni (on the left) and Atsani (on the right) as they moved across the central Pacific Ocean on Monday 17 August 2015 (animation also available here as an mp4). Goni has passed through the northern Mariana Islands and is forecast to fluctuate in intensity as it moves towards Asia. Atsani’s predicted path is towards the northwest; it is forecast to intensify to a Category 5 Super Typhoon. Both storms are moving across very warm ocean waters (Goni, Atsani), and deep layer wind shear values are low (below). Sea Surface Ttemperature and Wind Shear products are available from the CIMSS Triopical Cyclones site.

Satellite-derived Wind Shear over the Pacific Ocean, 1800 UTC 17 August 2015 [click to enlarge]

Satellite-derived Wind Shear over the Pacific Ocean, 1800 UTC 17 August 2015 [click to enlarge]

Late in the day on 17 August, a comparison of MTSAT-2 infrared (10.8 µm) and DMSP SSMIS microwave (85 GHz) imagery of Category 3 Typhoon Atsani around 2232 UTC (below) showed a rather ragged-looking eye on the infrared image and evidence of a eyewall replacement cycle (ERC) occurring on the microwave image. The ERC process often indicates that a change in tropical cyclone intensity will soon take place.

MTSAT-2 infrared (10.8 µm) and DMSP SSMIS microwave (85 GHz) images of Typhoon Atsani [click to enlarge]

MTSAT-2 infrared (10.8 µm) and DMSP SSMIS microwave (85 GHz) images of Typhoon Atsani [click to enlarge]

What is remarkable in this case of “twin typhoons” in the West Pacific basin is that the MIMIC-TC product indicated that both Atsani and Goni were undergoing ERCs at about the same time (below).

MIMIC-TC product for Typhoon Atsani [click to enlarge]

MIMIC-TC product for Typhoon Atsani [click to enlarge]

MIMIC-TC product for Typhoon Goni [click to enlarge]

MIMIC-TC product for Typhoon Goni [click to enlarge]

A multi-day YouTube animation of Himawari-8 10.35 µm infrared imagery shows the upscale development of Goni and Atsani in the central Pacific. The loop runs from 13 August through 1200 UTC on 18 August.

Chan-Hom approaches the coast of China

July 10th, 2015


The video above shows 5 hours of Himawari-8 10.35 µm Infrared imagery from Typhoon Chan-Hom as it moves through the Yellow Sea towards the coast of China (original animated gif here; mp4 here). The location of Shanghai is indicated in the first frame, and this blog post talks about the history of typhoon landfalls near Shanghai. The appearance of the storm in the animation above is relatively constant.

Himawari-8 10.35 µm infrared imagery, 1447-2002 UTC on 6 July 2015 (Click to animate)

Himawari-8 6.2 µm (top), 6.9 µm (middle) and 7.3 µm (bottom) water vapor infrared imagery, 0000 UTC 8 July 2015 – 1500 UTC 10 July 2015 (click to animate)

The three water vapor channels from Himawari-8, above, over the course of the past 3 days show a steady northwestward motion and a decrease in the cold cloud tops surrounding the storm, consistent with the weakening that has been observed after peak intensity at ~1500 UTC on July 9. Typhoon Nangka remains southeast of Chan-Hom; Typhoon Linfa has dissipated after having made landfall over south China. Chan-Hom’s path (below) is over progressively colder water and significant intensification is not expected before landfall.

Sea-Surface Temperatures over the Yellow Sea, along with Chan-Hom's past and projected path (Click to enlarge)

Sea-Surface Temperatures over the Yellow Sea, along with Chan-Hom’s past and projected path (click to enlarge)

A DMSP SSMIS 85 GHz microwave image at 0946 UTC on 10 July, below, showed that Category 3 Typhoon Chan-Hom was undergoing an eyewall replacement cycle as the small inner eyewall was being replaced by a much larger outer eyewall. Also on the image are 1244 UTC Metop ASCAT surface scatterometer winds, which displayed a large area with winds in the 50-59.9 knot range along the western periphery of the tropical cyclone.

DMSP SSMIS microwave image at 0946 UTC, and Metop ASCAT winds at 1244 UTC (click to enlarge)

DMSP SSMIS microwave image at 0946 UTC, and Metop ASCAT winds at 1244 UTC (click to enlarge)

Tropical Storm Ela east of Hawai’i

July 9th, 2015
Suomi NPP VIIRS visible (0.64 µm) and Infrared (11.45 µm) images of Tropical Depression 4E at 2224 UTC on 08 July

Suomi NPP VIIRS visible (0.64 µm) and Infrared (11.45 µm) images of Tropical Depression 4E at 2224 UTC on 08 July

Tropical Storm Ela began as Tropical Depression 4E about 900 miles east of Hilo, Hawai’i around 03 UTC on 08 July 2015. A comparison of daytime images of Suomi NPP VIIRS 0.64 µm Visible channel and 11.45 µm Infrared channel images (above) showed the somewhat disorganized appearance of TD 4E at 2224 UTC on 08 July — the low-level circulation center (LLCC) was located to the southwest of the clusters of deep convection associated with the system.

About 12 hours later, a nighttime comparison of VIIRS 0.7 µm Day/Night Band (DNB) and 11.45 µm Infrared channel images at 1052 UTC on 09 July (below) continued to show a similar disconnect between the LLCC and clusters of deep convection in the eastern semicircle of recently-upgraded Tropical Storm Ela. The coldest cloud-top IR brightness temperature in the convection closest to the storm center was -78º C. Even though the Moon was in the Waning Crescent phase (at 43% of Full), it still provided enough illumination to aid in the location of the LLCC, as noted in a discussion issued by the CPHC:

TROPICAL STORM ELA DISCUSSION NUMBER   7
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP042015
500 AM HST THU JUL 09 2015

A 1052Z VIIRS DAY/NIGHT BAND IMAGE WAS INSTRUMENTAL IN HELPING TO LOCATE THE PARTIALLY EXPOSED CENTER OF ELA THIS MORNING.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared (11.45 µm) images of Tropical Storm Ela at 1052 UTC on 09 July

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared (11.45 µm) images of Tropical Storm Ela at 1052 UTC on 09 July

According to satellite-derived winds products from the CIMSS Tropical Cyclones site, there was strong divergence and a well-defined outflow channel in the northern quadrant of Ela (below), whose center was located at 19.3º N 145.1º W at 09 UTC on 09 July.

GOES-15 water vapor (6.5 µm) images with satellite wind derived upper tropospheric divergence and winds

GOES-15 water vapor (6.5 µm) images with satellite wind derived upper tropospheric divergence and winds

The reason that the LLCC remained exposed from the elements of deep convection was the fact that Ela was encountering increasing amounts of southwesterly deep-layer wind shear as it tracked northwestward  (below).

GOES-15 Infrared (10.7 µm) images, with an overlay of deep-layer wind shear at 18 UTC on 09 July

GOES-15 Infrared (10.7 µm) images, with an overlay of deep-layer wind shear at 18 UTC on 09 July

========================= Added July 10 2015 ============================

The southwesterly shear over the storm decoupled the surface circulation from the overlying convection, and Ela was downgraded to a depression early on 10 July 2015. The 0700 UTC 10 July 2015 image below shows ASCAT Scatterometer winds depicting a low-level swirl well east of Hawai’i; deep convection with the system is hundreds of kilometers to the northeast.

ASCAT Scatterometer winds and GOES-15 infrared (10.7 µm) imagery, 0700 UTC 10 July 2015

ASCAT Scatterometer winds and GOES-15 infrared (10.7 µm) imagery, 0700 UTC 10 July 2015 (Click to enlarge)