Tropical Depression (update: Tropical Storm Surigae) over the western Pacific

April 13th, 2021 |

Himwari-8 Clean Window (10.41 µm) Band 13 Infrared imagery, 1220 – 2050 UTC on 13 April 2021 (Click to animate)

Himawari-8 Window Channel infrared imagery (10.41 µm), above, shows a well-defined tropical disturbance (Tropical Depression #2 has become become Tropical Storm Surigae by 0900 UTC on 14 April; this website shows Pacific basin names and includes audio pronunciation examples) moving between Yap and Palau in the western Pacific to the southwest of Guam. The disturbed weather in this region has persisted for many days as it has moved towards the west-northwest, as shown in the rocking MIMIC Total Precipitable Water animation below.

10-day animation of MIMIC Total Precipitable Water over the western Pacific Ocean, 2-12 April 2021 (Click to animate)

NOAA-20 NUCAPS estimates of tropopause Heights, below, show the storm in a region with a very high tropopause, around 120 hPa. The system is moving towards a region with similarly high tropopauses.

Himawari-8 Clean Window (10.41 µm) infrared imagery overlain with NUCAPS estimates of Tropopause Heights, 1540 UTC on 13 April 2021 (Click to enlarge)

Water Vapor imagery (6.24 µm and 7.3 µm) from near sunrise of 14 April show moist air in the immediate environment surrounding the storm (Link).  Visible imagery at sunrise on 14 April, below, show strong and persistent deep convection.

Himawari-8 Visible (0.64 µm) imagery, 2027 – 2114 UTC on 13 April 2021 (Click to enlarge)


It is interesting to note that during the ~12 hours prior to the disturbance (dubbed Tropical Invest 94W) being named Tropical Depression 02W at 12 UTC on 13 April, 2.5-minute interval Himawari-8 Visible (0.64 µm) images from 0002-0802 UTC (below) revealed a trio of low-level vorticies circulating around the incipient storm center. The northernmost vortex appeared to play a role in the initiation of a small cluster of sheared convection. While an exposed low-level circulation center is common in deteriorating highly-sheared tropical cyclones, the presence of 3 vortices during the formative stages of development is rather unusual.

Himawari-8 Visible (0.64 µm) images [click to play animation | MP4]

Himawari-8 Visible (0.64 µm) images [click to play animation | MP4]


Imagery from the CIMSS Tropical Weather Site (link), below, shows the system in a region of very warm Sea Surface Temperatures and modest shear.  Strengthening is forecast as it moves towards the Philippines.

Screencaptures from the CIMSS Tropical Weather Website ca. 2100 UTC on 13 April 2021 (Click to enlarge)


Himawari-8 Imagery courtesy of JMA, the Japan Meteorological Agency.

CSPP GeoSphere views of the Soufriere Eruption on 11 April 2021

April 11th, 2021 |

GOES-16 True Color Imagery, 1210-1600 UTC on 11 April 2021 (click to animate)

CSPP GeoSphere allows a user to view True Color imagery (and individual GOES-16 bands) in real time using data from the four GOES-16 domains:  Full Disk, CONUS, and Mesoscale Sectors 1 and 2.  The animation above shows the 1330 UTC eruption (11 April 2021) of Soufriere, one of a series of eruptions from that volcano (as discussed here and elsewhere).  The ash emitted by the short (duration) eruption then moves westward towards Barbados, following upper-level winds.  (Low-level winds are easterly).  The rapid ascent of the ash cloud is documented below, showing 4 images from the Full Disk imagery at 1320, 1330, 1340 and 1350 UTC.

GOES-16 True Color Imagery, at 1320, 1330, 1340 and 1350 UTC on 11 April 2021 (click to animate)

Rapid changes suggest Mesoscale imagery would be useful.  Indeed, volcanic events area ranked #2 on the GOES-R MDS Priority List, after only a SPC High/Moderate Risk for Severe weather.  Thus, mesoscale Sector 2 imagery was available over the area.   That is shown below and it better captures the time of the eruption and better resolves the ascent through the troposphere.

GOES-16 Mesoscale sector 2 True Color Imagery, 1320-1347 UTC (Click to animate)

Seven consecutive zoomed-in 1-minute images are shown below, from 1329 through 1336 UTC on 11 April (with the map removed; CSPPGeo link used here; a similar animation from the CIRA Slider is here.) They show the initial stages of this particular eruption.  A Pileus cap is obvious at the top of the eruption at 1329 UTC. (Animation available here as an mp4).

GOES-16 Mesoscale sector 2 True Color Imagery, 1329-1336 UTC (Click to enlarge)

Quantitative information on some aspects of this series of events can be found at the VOLCAT website.  You can also find information at the Washington DC VAAC (Volcanic Ash Advisory Center).

Interpreting SAR data over the Bering Sea

April 8th, 2021 |

GOES-17 ABI Band 2 (0.64 µm) and Band 5 (1.61 µm) at 1740 UTC on 8 April 2021 (Click to enlarge)

The toggle above shows GOES-17 ABI Band 2 (“Red Visible” at 0.64 µm) and Band 5 (“Snow/Ice” at 1.61 µm) imagery at 1740 UTC on 8 April 2021. 60ºN and 170ºW lat/lon lines are included in yellow, as well as Nunivak Island.  There is evidence of sea ice extending from south of Nunivak northwestward;  visible 0.64 µm imagery  shows much greater reflectance compared to 1.61 µm snow/ice imagery.  It’s much harder to view the ice edge in the snow/ice channel because reflectances in that channel for ice and water are similar.

Compare the toggle above to the Sentinel-1A Synthetic Aperture Radar (SAR) image at 1735 UTC on 8 April 2021, shown below.   The stark wind difference (red vs. blue) in the SAR wind image below is in reality a change in ocean state, with ice over the red region and open water over the blue.  (Here is the Sea Ice analysis for 8 April from the Alaska Sea Ice Program (ASIP)).  Interpretation of SAR winds requires a knowledge of the presence of ice.

Sentinel 1-A analysis at 1735 UTC on 8 April 2021 (Click to enlarge)

Cyclone Seroja

April 5th, 2021 |

Himawari-8 ‘Target Area’ clean window infrared (10.41 µm) imagery, 1224 – 2018 UTC on 5 April 2021 (Click to animate)

Himawari-8 ‘Target Area’ imagery (with a 2.5-minute timestep) on 5 April show the evolution of Cyclone Seroja over the Timor Sea northwest of Australia. (Click here for an mp4 animation). Periodic bursts of deep convection (black and white in the color-enhancement) are apparent in the center of the storm. Analyses from the CIMSS Tropical Weather Site (link) show the storm in a region of warm Sea Surface Temperatures. Modest shear is present and it is changing the convective core of the storm in the animation above from circular to elongated over the 8-hour animation. However, strengthening is forecast.

Screen capture of SSTs over the Timor Sea, wind shear, and forecast path of Cyclone Seroja (Click to enlarge)

Visible imagery at sunrise on 6 April shows the evolution of the storm.

Himawari-8 visible (0.64 µm) imagery, 2152 – 2304 UTC on 5 April 2021 (Click to enlarge)

Himawari-8 imagery courtesy JMA. You can also view satellite imagery over the area from KMA.

Update 8 April

Himawari-8 imagery (10.41 µm), below, from 0300-1610 UTC on 8 April, show a large cirrus canopy initially over Seroja eroding (You can see the 0300 and 1610 UTC images alone toggling here) Can you tell from this infrared imagery where the storm center sits?

Himawari-8 clean window infrared (10.41 µm) (full disk) imagery, 0300 – 1610 UTC on 8 April 2021 (Click to animate)

This is certainly a case where microwave imagery can (and should!) be used to better pinpoint the circulation center.  ASMU-B imagery at 89 GHz (from here), below, storm-centered at 2307 UTC 7 April, 0207 8 April and 1143 UTC on 8 April show a storm center near 18ºS, 111.5ºE at around 1200 UTC on 8 April.  Here is the Himawari-8 Clean Window infrared at 1140 UTC.  Could you place the center near its microwave-suggested center using this infrared imagery?

AMSU-B imagery at 2307 UTC 7 April, 0206 8 April and 1143 8 April. Satellite Platform as indicated in the image. Click to enlarge)

Imagery from the CIMSS Tropical Website (link), below, show that Seroja on 8 April was traversing a region of low shear.  Sea surface temperatures at present under the storm are warm; however, the projected path of the storm is towards cooler ocean waters.  There is abundant upper-level divergence over the storm and to the northwest of Seroja as well.

Maps of atmospheric wind shear, sea-surface temperatures and upper-level divergence, ca. 1500 UTC on 8 April 2021. The path of the storm, and the projected path of the storm are also noted.

Radarsat-2 Synthetic Aperture Radar (SAR) wind data (from this website), shown below, from 1054 UTC on 8 April, can also be used to infer a circulation center.

Radarsat-2 SAR Data over Seroja, 1054 UTC on 8 April 2021 (Click to enlarge)