Transition of Typhoon Atsani into powerful post-tropical low

Typhoon Atsani transitions into extra-tropical low

20 August 2015 00:00 UTC and 25 August 12:00 UTC

Transition of Typhoon Atsani into powerful post-tropical low
Transition of Typhoon Atsani into powerful post-tropical low

In August Atsani transitioned from a Category 5 super typhoon into a powerful extra-tropical storm.

Last Updated

09 March 2021

Published on

20 August 2015

By NOAA Ocean Prediction Center, Scott Bachmeier (CIMSS ), Jochen Kerkmann (EUMETSAT) and HansPeter Roesli (Switzerland)

In mid-August there were two powerful typhoons in the Western Pacific — Goni and Atsani. While Typhoon Goni made landfall on the Japanese island of Kyushu on 25 August, Atsani circulated over the ocean and didn't make landfall.

On 19 August Atsani reached super typhoon status, with 1-minute sustained winds of 260 km/h (160 mph), and in the following days it started to weaken.

However, on 24–25 August, instead of dying out as it got caught up in the mid-latitude jet stream winds, it transformed into a powerful extra-tropical storm. It went from a storm that had a warm core, with a centre milder than the surrounding air, into a system with a cold core. The resulting storm reportedly produced hurricane-force winds and extremely high waves across the North Pacific (Credit: Mashable).

 Himawari-8, 25 August 2015, 12:00 UTC
Figure 1: Himawari-8, 25 August 2015, 12:00 UTC
Airmass RGB
Full Resolution
 
 Surface analysis, 25 August, Valid for 06:00 UTC
Figure 2: Surface analysis, 25 August, Valid for 06:00 UTC
Full Resolution
Animated gif on CIMSS Blog

The Himwari-8 Airmass imagery, Figure 1 and animation produced by NWSOPC (NOAA's Ocean Prediction Center), clearly shows that on 25 August Atsani started to transition into an intense extra-tropical low. On the animation, a graphic is included that highlights the main differences between a tropical and extra-tropical low.

Surface analysis from the Ocean Prediction Center (Figure 2) indicated that the extra-tropical storm deepened to a minimum central pressure of 957 hPa at 12:00 UTC on 25 August, and was producing hurricane-force winds until 00:00 UTC on 26 August (Credit: CIMSS Blog).

Figure 3 shows the Night Microphysics RGB product, for the same situation as shown in Figure 1. This RGB product is mainly used to identify clouds at different levels, including low-level clouds, which are not as visible in the Airmass RGB (Figure 1).

In Figure 3 two images are shown: one RGB with the SEVIRI standard tuning (green component (IR11.2-IR3.9) is displayed for a range of 0 to 10 K), and the other one with a tuning that is appropriate for the AHI instrument (green component is displayed for a range of –5 to +5 K). This shift of the range of the green component is needed as the AHI band 7 (IR3.9) is not affected by CO2 absorption. In the tuned RGB product, low-level clouds can be easily identified by their green colour.

Image enhancement comparison

Himawari-8, Night Microphysics RGB, 25 August 12:00 UTC with a proper tuning of the green (IR11.2–IR8.6) beam compare1
compare2
 

Figure 3: In the tuned RGB product (right), low-level clouds can be easily identified by their green colour

 Himawari-8 Band 3, 20 August 00:02 UTC
Figure 4: Himawari-8 Band 3, 20 August 00:02 UTC. Full resolution

Figure 4 shows typhoon Atsani at its full strength on 20 August 2015, 00:02 UTC.

On this day, Atsani was close to the Philippines. The image shows Band 3 of the AHI instrument (0.64 µ), which is the only channel that has a high resolution of 0.5 km.

 
 

Related Content

The transition of Typhoon Atsani to a strong extra-tropical storm (CIMSS Blog)
How Super Typhoon Atsani transformed from one type of monster storm into another (Mashable)