Typhoon Doksuri moved between the Philippines and Taiwan late on 26 July 2023 as it approached mainland China. Both Sentinel-1A and RCM-3 overflew the storm shortly after 2200 UTC on 26 July, and those two scenes are shown above in concert with a Band 13 Himawari-9 Clean Window infrared (10.4 µm) imagery. (All SAR observations of Doksuri are available here). The asymmetric nature of the storm is very notable, with winds exceeding 70 knots in the eyewall to the north and east of the storm (winds exceed 80 knots in the convective band farther to the east — the region of white in the wind enhancement used). In contrast, winds in the western eyewall are between 35 and 50 knots — and there is a curious wind speed minimum just west of the eyewall!

A MIMIC-TC animation from 26 July 2023, below, also shows the marked asymmetry in the storm. Doksuri’s path was right along the northern coastline of of Luzon, the northernmost large island of the Philippines. Mountain ranges on that island may have influenced the structure of the storm.

Wind shear over the system at the time of the SAR overpasses was light, but would be acting to displace the convection south and east of the storm center, as observed. The image below was taken from the CIMSS Tropical Weather Site.

For current information on Doksuri, refer to the Joint Typhoon Warning Center, the Tokyo RSMC, the CIRA Real-Time Tropical Website and the CIMSS Tropical Weather Site.

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GOES-18 “Red” Visible (0.64 µm) images [click to play animated GIF | MP4]

1-minute Mesoscale Domain Sector GOES-18 (GOES-West) “Red” Visible (0.64 µm) images (above) showed the development of thunderstorms across much of the eastern portion of Interior Alaska on 24 July 2023. The large satellite viewing angle — which is 73.5 degrees for Fairbanks (station identifier PAFA) — provided an oblique perspective that nicely displayed the vertical buildup of towering cumulus as well as the formation of thunderstorm anvils.

In the corresponding 1-minute GOES-18 “Clean” Infrared Window (10.3 µm) images (below), the coldest thunderstorm tops exhibited infrared brightness temperatures around -60ºC (darker shades of red).

GOES-18 “Clean” Infrared Window (10.3 µm) images [click to play animated GIF | MP4]

Parallax displacement direction (green arrows) and displacement magnitude (in km, red) for a 30000-ft cloud top feature on GOES-18 imagery [click to enlarge] 

When viewing satellite imagery at high latitudes, it is important to keep parallax in mind — so for the thunderstorms that produced wind damage east-southeast and southeast of Fairbanks at 0315 UTC and 0330 UTC, their cloud tops (at an average altitude around 30000 ft) were actually displayed about 32 km (20 miles) to the north-northwest of their true location over the surface (above).

The parallax displacement was apparent in a closer view of 1-minue GOES-18 Visible and Infrared images, centered near Fairbanks, with plots of Severe Thunderstorm Warning polygons (below). 

GOES-18 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images, with Severe Thunderstorm Warning polygons plotted in yellow [click to play animated GIF | MP4]

Pulses of overshooting tops were evident with many of these thunderstorms, such as one seen just northeast of Eielson Air Force Base (PAEI) in a toggle between GOES-18 Visible and Infrared images at 0244 UTC (below) — which was about 30 minutes prior to the first report of damaging winds 15 miles ESE of Fairbanks.

GOES-18 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images at 0244 UTC on 25 July [click to enlarge]

Cursor-sampled values of GOES-18 infrared (10.3 µm) brightness temperature (white), Cloud Top Temperature (cyan) and Cloud Top Height (green) for a thunderstorm overshooting top at 0244  UTC on 25 July [click to enlarge]

For the overshooting top northeast of PAEI at 0244 UTC, cursor-sampled values of GOES-18 infrared (10.3 µm) brightness temperature, Cloud Top Temperature and Cloud Top Height were -61.85ºC, -63.93ºC and 38669.15 feet, respectively (above) — which, according to a plot of 0000 UTC rawinsonde data from Fairbanks (below), represented an altitude just above the Equilibrium Level (EL) of a Most Unstable (MU) air parcel.

Plot of rawinsonde data from Fairbanks, Alaska at 0000 UTC on 25 July [click to enlarge]

These thunderstorms occurred on a day that Fairbanks set a new daily record high temperature of 90ºF — and a Cooperative Observer in the Fairbanks area reported a high temperature of 92ºF (Regional Temperarture and Precipitation).

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The Joint Typhoon Warning Center (JTWC) website has for more than a day been tracking invest number 91W, shown above. The feature is circled in yellow, meaning development is unlikely in the next 24 hours. What satellite data might be used to make that determination?

MIMIC Total Precipitable water fields, for the 24 hours ending at 1600 UTC on 24 July 2023, below, show an area rich in tropical moisture, and a broad, diffuse, cyclonic circulation is present between 140 and 150^o E, an between the Equator and 10^oN. In other words, there is plenty of moisture here and one can therefore infer a lack of dry air to impede convection. Are there observations to support the presence of a cyclonic circulation? Motion in the MIMIC fields is a by-product of advection of MIRS Total Precipitable Water fields (computed from individual data swaths from low-earth-orbit — LEO — satellites) by the GFS model (see this training on MIMIC).

Advanced Scatterometer (ASCAT) data from Metop-C and Metop-B (from this NOAA/NESDIS/STAR website), below, shows a cyclonic circulation with southwest winds between 2^o and 6^o N, and southeast winds from 6^oN to 10^oN, around near 147^o E at around 0000 UTC on 24 July 2023. The 1200 UTC imagery, below, doesn’t quite show a circulation in the same region, but it’s hard to tell how well it might have been sampled.

Tropical Cyclones typically form in regions of low shear. Estimates of shear are available at the SSEC/CIMSS Tropical Website (direct link), as are convergence/vorticity analyses, shown in a toggle below. For the region between 0 and 10^oN, 140 to 150 ^oE, there is low-level vorticity (not as concentrated as in the region of Typoon Doksuri, of course) near a narrow ribbon of low shear values (larger shear values are Equatorward of the vorticity center). Low-level convergence and upper-level divergence in the region are weak and do not appear to be linked however.

Himawari-9 Upper-level and lower-level Water Vapor imagery, below (Band 10, 7.34 µm, on the left and Band 8, 6.24 µm, on the right) from 1000 to 1500 UTC shows widespread convection in the square bordered by 140 and 150 oE and 0 and 10oN. No widespread dry air is present. Much of the convection is south and east of the vorticity center.

Future information on this invest (and on Typhoon Doksuri) can be viewed at the webpages of the Joint Typhoon Warning Center. The RSMC at Tokyo also has information on Western Pacific tropical cyclones. Forecasts are for 91W to move between Yap and Guam in the next days. The information presented here might help the reader decide for themselves whether or not the Invest will develop further.

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The image above shows International Space Station orbital paths over the western Pacific Ocean on 24 July 2023, computed from the TLE files and displayed using McIDAS. Note the orbital path at 1600 UTC that moves from mainland China southeastward over Taiwan and then to Indonesia. This is in close proximity to Typhoon Doksuri at that time. LIS lightning observations along this path, from 1602 to 1607 UTC, are shown below. Lightning strikes are detected within the outer rainbands of the typhoon, but no observations occur near the eyewall.

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