NOAA-20 VIIRS True Color image of Typhoon Yagi on 4 Sept 2024

PREFIRE sees the eye of Super Typhoon Yagi near peak intensity

This event occurred on September 5, 2024

Typhoon Yagi was the first Super Typhoon to develop in the Western North Pacific basin during the 2024 typhoon season. It affected the Philippines, China, Vietnam, Myanmar, Laos, Thailand, and other parts of Southeast Asia with damaging winds and devastating flooding. All told, Yagi caused over 800 fatalities and near $15 billion in damage, placing it among the top 10 most costly Western North Pacific typhoons on record.

Yagi intensified into a Category 5-equivalent super typhoon on 5 Sept 2024, becoming only the fourth category 5 storm on record in the South China Sea. The animation below shows that at approximately 12:40 UTC on 5 Sept 2024, PREFIRE-SAT2 passed directly over the center of the storm. According to the Joint Typhoon Warning Center, Yagi had a minimum central pressure of 928 mb and maximum sustained winds of 125 kt at 12:00 UTC, then strengthened to 907 mb (145 kt) at 18:00 UTC, so the PREFIRE overpass occurred as Yagi was deepening to its maximum strength.

Himawari-9 animation of Typhoon Yagi with PREFIRE overpasses — Typhoon Yagi as seen by Himawari-9 AHI band 14 (11.2 µm) brightness temperature (BT) from 5 Sept 2024 11:00 – 15:20 UTC. A PREFIRE-SAT2 overpass of the typhoon is illustrated by the green-colored dots, with darker green shades indicating nearer times to the overpass and the pink dots indicating a ± 15-minute time window around the overpass.

The Thermal InfraRed Spectrometer (TIRS) on board each PREFIRE satellite is not an “imaging” instrument—it has moderate spatial and spectral resolution and gaps between its across-track fields of view. Despite these instrument characteristics, Yagi’s eye, central dense overcast (CDO), and outer rain bands can clearly be seen by PREFIRE! See the brightness temperature map on the right below. The map on the left shows a zoomed-in snapshot of Himawari-9 AHI data, with the cyan triangles marking the locations of PREFIRE scenes that are selected for further analysis.

Himawari-9 AHI and PREFIRE-SAT2 IR window channel brightness temperature from Typhoon Yagi overpass — (Left) Himawari-9 AHI band 14 (11.2 µm) brightness temperature (BT) and (right) PREFIRE-SAT2 channel 12 (10.98 µm) BT for PREFIRE-SAT2 overpass of Typhoon Yagi at approximately 12:40 UTC on 5 Sept 2024. On left panel, all PREFIRE-SAT2 ground tracks are shown in gray, with locations of spectra selected for further analysis marked with cyan triangles.

PREFIRE’s unique capabilities are illustrated by the radiance spectra in the plot below. The PREFIRE-TIRS2 measurements show that within Yagi’s clear, warm eye (red dots), relatively large amounts of radiation were emitted, with a sharp peak in the mid-infrared part of the spectrum. But nearby in the northern eyewall, TIRS2 measured much less outgoing infrared radiation, with a much flatter spectral slope that peaked at longer wavelengths in the mid-infrared region. Other areas of cold cloud tops—the southern CDO, southern cirrus shield (colder cloud top temperature), and southern rain band spectra—emit similarly low levels of radiation, but with subtle differences in their spectral shapes that may hold information on cloud properties and column water vapor differences.

PREFIRE-SAT2 radiance spectra plot for Typhoon Yagi overpass — PREFIRE-SAT2 radiance spectra from selected locations of Typhoon Yagi overpass. The top-to-bottom order of items in the plot legend matches the north-to-south order of spectra locations indicated with cyan triangles on the satellite image above. CDO is “central dense overcast” and CTT is “cloud top temperature”.

With this overpass, PREFIRE provided a unique spectrally- and spatially-resolved view of the radiation emitted by a super typhoon from mid- to far-infrared wavelengths. Although PREFIRE’s primary focus is the Earth’s polar regions, its Level-1B products are available globally and can provide insight into radiative processes throughout the world.