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Tropical Storm Nepartak approaches Japan

As the games of the 2021 Olympics progress, a weakening Tropical Storm Nepartak is moving over coastal waters to the east of Honshu, the main island of Japan. The Total Precipitable Water imagery, above, from MIMIC TPW, shows a plume of moisture wrapped around the circulation center. Himawari-8 Clean Window... Read More

MIMIC microwave estimates of Total Precipitable Water, 1800 UTC on 26 July 2021 (Click to enlarge)

As the games of the 2021 Olympics progress, a weakening Tropical Storm Nepartak is moving over coastal waters to the east of Honshu, the main island of Japan. The Total Precipitable Water imagery, above, from MIMIC TPW, shows a plume of moisture wrapped around the circulation center. Himawari-8 Clean Window infrared (10.41 µm) imagery, below , from the Himawari-8 Target scene (courtesy of JMA; here’s a link to more JMA satellite imagery), shows the progression of the storm.

Himawari-8 Band 13 Clean Window Infrared (10.41 µm) imagery, 1712 – 2327 UTC, 26 July 2021 (Click to animate)

The forecast from the Joint Typhoon Warning Center (JTWC) as of 1800 UTC has the weakening storm backing into northern Honshu (forecast track; it’s also available from JMA). As of 2300 UTC, the center of Nepartak had moved north to Tokyo’s latitude, and convective bands on the west side of the storm are affecting areas around Tokyo, Yokohama, Sagami Bay and Chiba prefecture. Interests in Japan should monitor closely the progress of this storm.


Visible imagery from shortly after sunrise on Tuesday 27 July in Japan shows the storm to the east of Japan; very little convection is within the storm center.

Himawari-8 Visible Image (0.64 µm), 0024 UTC 27 July 2021

Metop-A overflew Japan at around 1040 UTC on 27 July. Scatterometry (source) showed the wind structure of the storm very nicely.

MetopA Scatterometer winds, 1041 UTC on 27 July 2021 (Click to enlarge)

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Tropical disturbance off the US Southeast Coast

The National Hurricane Center is monitoring an area of disturbed weather over the western Atlantic, to the north of the Bahamas and south of Cape Hatteras. The three-hour animation from the CSPP GeoSphere site (link, above), shows convection and a small low-level cyclonic circulation. This system is drifting to the... Read More

CSPP GeoSphere animation, 1240-1550 UTC on 25 July 2021

The National Hurricane Center is monitoring an area of disturbed weather over the western Atlantic, to the north of the Bahamas and south of Cape Hatteras. The three-hour animation from the CSPP GeoSphere site (link, above), shows convection and a small low-level cyclonic circulation. This system is drifting to the east, towards Florida, and is in an environment of small values of vertical wind shear (the analysis below is from the CIMSS Tropical Weather Site) that could augur further development. Refer to the pages of the National Hurricane Center for more information.

200-850 Shear Values, 1400 UTC on 25 July 2021. The disturbance center is denoted with an I.

The Day Night Band image from Suomi NPP, below, from the early morning of 25 July 2021, (from the VIIRS Today website) shows the storm under the waning Buck Full Moon. Compare that to the NOAA-20 Day Night Band image from 24 July, the night before (link): the amount of convection decreased between 24 and 25 July.

Suomi NPP Day Night Band imagery, 25 July 2021

On the morning of 26 July 2021, the disturbance is moving into Florida/Georgia. Convection associated with the system is not over its center. (CSPP Geosphere link)

CSPP Geosphere animation, 1320-1610 UTC on 26 July 2021

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Moist air over the tropical western Pacific Ocean

Microwave estimates of total precipitable water over the western Pacific Ocean (available here) show a moist airmass — out of which Typhoon In-Fa (seen near Taiwan in the animation) emerged — over the western Pacific Ocean. (The circulation of Tropical cyclone Cempaka is also apparent near the Gulf of Tonkin)... Read More

MIMIC Total Precipitable Water, 0000 UTC 21 July – 1200 UTC 22 July

Microwave estimates of total precipitable water over the western Pacific Ocean (available here) show a moist airmass — out of which Typhoon In-Fa (seen near Taiwan in the animation) emerged — over the western Pacific Ocean. (The circulation of Tropical cyclone Cempaka is also apparent near the Gulf of Tonkin) This rich moisture has led to very heavy rains and Flash Flood alerts on the island of Guam (at 13.4ºN, 144.5ºE). Are there any indications that a new tropical cyclone will emerge out of the moisture?

The toggle below shows Himawari-8 10.41 µm “Clean Window” infrared imagery (notice In-Fa in the northwest part of the image). A distinct trough is apparent in the scatterometery north of the Marianas islands (and north of 20ºN latitude), with west-southwesterly surface winds bordered by east-southeasterlies to the north. Weaker winds are indicated south of Guam. (For a recent primer on Scatterometer winds, click here; ASCAT winds can be found online here)

ASCAT Scatterometry winds and Himawari-8 Band 13 infrared (10.41 µm)imagery, 1200 UTC on 22 July 2021

NOAA-20 overflew this region at 1600 UTC on 22 July. The imagery below shows Tropopause Heights as well as Total Precipitable water — along with Band 13 imagery (over a different location) at that time. NUCAPS estimates of TPW are in the 60-70 mm range (in agreement with the MIMIC animation above); Very high tropopauses are Equatorward of 20 N Latitude.

A ribbon of small wind shear exists, as shown in the 200-850 wind shear analysis below, taken from the CIMSS Tropical Website. Meteorologists continue to monitor this region of tropical activity.

200-850 mb wind shear, 1800 UTC on 22 July 2021, over the western Pacific Ocean.

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Aerosol Optical Depth and surface visibility

The image above shows the Level 2 GOES-R product, Aerosol Optical Depth (AOD), a product created in clear skies, overlain with the GOES-16 Visible imagery from the same time. AOD measures the extinction of light via scattering and absorption by small particles in the atmosphere, and it can be used... Read More

GOES-16 Aerosol Optical Depth and GOES-16 Band 2 Visible (0.64 µm) imagery, 1401 UTC on 22 July 2021

The image above shows the Level 2 GOES-R product, Aerosol Optical Depth (AOD), a product created in clear skies, overlain with the GOES-16 Visible imagery from the same time. AOD measures the extinction of light via scattering and absorption by small particles in the atmosphere, and it can be used as a proxy for particles smaller than 2.5 µm in diameter (PM25). The red regions show the highest values. The plot below shows surface observations of ceilings (plotted to the left of the circles) and visibility (plotted below the circles) at the same time as the AOD image above. Is there a relationship?

Look at the string of lower visibilities stretching along the North Carolina/South Carolina border, extending westward to Tennessee and then northward into Illinois. This is the region where AOD exceeds about 0.4 — cyan in the enhancement used above. In this instance, AOD can be used to highlight regions where surface visibilities are most restricted by aerosols. (Some of these aerosols are likely from smoke. However, this product does not tell you what kind of aerosol is there, only that it is causing extinction).

Surface observations of ceilings and visibilities, 1401 UTC on 22 July 2021

The toggle below steps through the observations, AOD, and Visible imagery at 1401 UTC. Kudos to Frank Alsheimer, the Science and Operations Office (SOO) in Columbia SC, for alerting us to this case.

Surface observations of ceilings and visibilities, GOES-16 Aerosol Optical Depth and GOES-16 Band 2 Visible (0.64 µm) imagery, 1401 UTC on 22 July 2021

True-color imagery, below, (saved in this case from the CSPP Geosphere site, using this link) also shows the extent of the aerosol-rich air.

GOES-16 ‘True-Color’ imagery at 1401 UTC on 22 July 2021

The relationship between AOD values and surface visibility persisted on 23 July 2021, below.

GOES-16 Aerosol Optical Depth and GOES-16 Band 2 Visible (0.64 µm) imagery, 1201 UTC on 23 July 2021

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