Tropical Cyclone Ashobaa

Tropical Cyclone Ashobaa

6 June 2015 06:30 UTC—11 June 06:00 UTC

Tropical Cyclone Ashobaa
Tropical Cyclone Ashobaa

In early June 2015 Tropical Cyclone Ashobaa formed over the Indian Ocean, then headed towards Oman.

Last Updated

23 February 2022

Published on

06 June 2015

By Hilal Al-Hajri and Shima Al-Yazidi (PACA), Jochen Kerkmann (EUMETSAT), HansPeter Roesli (Switzerland)

After forming as tropical storm off the Indian subcontinent, Ashobaa moved over the Arabian Sea, becoming a Category 1 cyclone. According to the Oman Department of Meteorology, the island of Masirah (off the east coast of Oman) received 239.4mm of rain during the three days that Ashobaa affected the country.

The progress of the tropical cyclone can be seen in the Meteosat-7 infrared animation, 5 June 12:00 UTC–15 June 06:00 UTC, from sudden birth on 5 June, explosive on 7 June, to slow dissipation from 10 to 15 June, after landfall there was recurrent severe convection near Masirah Island.

 Meteosat-7 sandwich product, 8 June 12:00 UTC (IR blended with VIS background image)
Figure 1: Meteosat-7 sandwich product, 8 June 12:00 UTC (IR blended with VIS background image)
 
 
 Meteosat-7 Visible, 6 June 06:30 UTC–10 June 13:00 UTC (animated gif)
Figure 2: Meteosat-7 Visible, 6 June 06:30 UTC–10 June 13:00 UTC (animated gif). Full Resolution image , Meteosat-7 Visible, 8 June 02:00 UTC

Ashobaa started to develop in the Indian Ocean, near Indian subcontinent, and was classified as a low pressure on 5 June. It was 1400km away from the Oman coast.

The low pressure started to intensify and move north to north west. On 7 June the surface wind around the centre reached between 46–56km/h ( 25–30kts) and the system was classified as a deep depression.

At that time the system was still travelling north to north west and was located 1200km away from the Oman coast.

On 8 June the system started to intensify very quickly (Figure 2) and became a named tropical storm (Ashobaa), see Met-10 Dust RGB image with ECMWF 10m model winds overlaid (Credit: EUMeTrain). The wind speed around the centre was between 64–74km/h (35–40kts) and the movement became more west to north west, see also Day Microphysics RGB (8 June 11:00 UTC) from the Indian Meteorological Agency's Insat 3D satellite.

The Metop AVHRR image (Figure 3) shows the extensive, high-level cirrus outflow from the relatively small tropical storm.

 Metop-A AVHRR IR10.8 image blended on the Night Microphysics background image, 8 June 17:05 UTC
Figure 3: Metop-A AVHRR IR10.8 image blended on the Night Microphysics background image, 8 June 17:05 UTC. Full Resolution

On day-night band imagery from NOAA's Suomi-NPP satellite, from 8 June at 20:45 UTC the cyclone's structure could be clearly seen.

On 9 June the tropical storm moved closer to Oman — approximately 500km off the coast. At that time the advocated high and medium cloud touched the Oman coast and sea condition were rough, with waves reaching 3.5m.

For tropical storms like Ashobaa it is often difficult to locate the centre (defined as low level circulation centre) of the system in simple VIS or IR images. In these cases, it is recommendable to use microwave imagery like the 89 GHz Channel from MHS on Metop, or comparable channels on other satellites like the 37 or 85 GHz channels on TMI, or the 85 GHz channel on SSMI, or, even better, to use the wind vectors from scatterometer instruments like ASCAT to locate the centre of the cyclone. For more info, have a look at the lecture from Sheldon Kusselson (NOAA) , presented in 2012 during a satellite training workshop in Pretoria, South Africa

Figure 4 shows the AVHRR IR image from 9 June 05:29 UTC and compares it to the 89 GHz image from MHS. The centre of the cyclone is not visible on the IR image but clearly appears on the MHS image.

Image comparison

Metop-A MHS Channel 01, 9 June 05:29 UTC compare1
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Figure 4: Comparison of Metop-A infrared and microwave images.

Image comparison

Metop-A Visible with ASCAT winds overlaid, 10 June 05:18 UTC compare1
compare2
 

Figure 5: Comparison of Metop-A visible images, on which the second image has ASCAT winds overlaid.

Image comparison

Meteosat-10 Dust RGB, 10 June 02:00 UTC compare1
compare2
 

Figure 8: Comparison of Meteosat-10 images showing the dust.