Cyclone Chapala continued its unusual approach towards Yemen on the southwestern edge of the Arabian Peninsula. Early on 2 November, the storm has passed just north of the Island of Socotra and entered the Gulf of Aden. METOP-B overflew the storm at ~0615 UTC on 2 November; Visible and Infrared data, above, show a still-compact storm with an obvious eye ringed by cold cloud tops (the coldest brightness temperatures are near -75º C) tucked into the mouth of the Gulf of Aden. Wind shear in the region is very low and sea-surface temperatures are warm. The morphed microwave imagery, below (taken from this site), indicates that the eyewall brushed the island of Socotra as it passed (a comparison of Meteosat-7 Infrared and DMSP SSMIS microwave images around 15 UTC on 01 November can be seen here).

Subsequent microwave imagery, below, for the 24 hours ending 1200 UTC on 2 November (the image below overlaps the one above) show a decrease in the eyewall structure and intensity.

Satellite-based intensity estimates at around 0000 UTC on 2 November (link) suggest a central mean sea-level pressure around 940 mb with sustained winds near 120 knots. The 0000 UTC Meteosat-7 image is shown below.

Suomi NPP overflew the region shortly after 2100 UTC on 1 November, and the Day/Night Band imagery from VIIRS is shown below, toggled with the 11.45 µm Infrared imagery. The storm is centered just northwest of Socotra; mesovortices are evident within the eye, as are overshooting tops in the eyewall convection; the bright streak seen on the Day/Night Band image is a region of the western eyewall illuminated by intense lightning activity. Zoomed-out versions of the imagery are available here for Day/Night Band and here for 11.45 µm Infrared. (VIIRS Imagery courtesy William Straka, SSEC/CIMSS).

A comparison of Meteosat-7 Infrared and DMSP SSMIS Microwave images around 1530 UTC on 2 November, below, showed the northern edge of the eyewall very near to the coast of Yemen.

At landfall, below, as viewed by Suomi NPP’s VIIRS instrument and a timely overpass, the eye of the storm had filled. The change in storm structure prior to landfall was very apparent in this toggle of two METOP Infrared images, at 0558 and 1644 UTC on 2 November. However, Meteosat-7 Infrared images showed that there was a large convective burst that developed as Chapala made landfall. Chapala was the first tropical cyclone on record to make landfall in Yemen while still at hurricane intensity.

A 6-day animation of the storm using VIIRS true-color imagery from RealEarth can be seen here. Cyclone Chapala is also discussed in this blog post.

===== 05 November Update =====

A 14-day animation of UK Met Office OSTIA Sea Surface Temperature, below, reveals the cold wake of upwelling water (yellow color enhancement) following the passage of Hurricane Chapala.

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Himawari-8 (Imagery courtesy of JMA) captured the northward march of three sets of Internal Waves in the Banda Sea in late October, as shown above (MODIS True Color Imagery showed the waves as well). Because the internal waves affect the ocean surface, sun glint can make them visible via methods described here. The fine spatial and temporal resolution of Himawari-8 (0.5 km for Band 3/0.64µm, 10-minute imagery) allows for a good description of the northward speed of the waves: approximately 10 km/hour.

MTSAT-2 (scheduled to become the backup satellite on Friday 4 December 2015 as Himawari-8 takes over operational duties; MTSAT-1 is to be decommissioned that day because of fuel limitations) and COMS-1 also viewed the waves, as shown below. Sun glint allowed MTSAT-2 to view only three scenes (3:32, 4:32 and 5:32 UTC). COMS-1, above the Equator at 128º E, farther west than MTSAT-2 (at 145º E), viewed the waves earlier (because sunglint was present over the scene earlier). Both MTSAT-2 and COMS-1 visible channels have nominal resolution of only 1 km.

Hat Tip to Mike Ziobro, NWS Guam, for showing us these very interesting waves!

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Tropical Cyclone Chapala is poised to make an unusual landfall on the Arabian Penisula over the weekend. The Suomi NPP VIIRS Day Night Band Imagery (courtesy William Straka, SSEC/CIMSS), above, from 2102 UTC on 29 October, shows a compact storm with curved bands of strong convection around an apparent eye. A more zoomed-in version of the storm in the infrared (A Zoomed in version of the Day Night band is here), shows very cold cloud tops.

Data from the CIMSS Tropical Page shows the environment in which Chapala strengthened will become progressively less favorable as the storm approaches land. The MIMIC Total Precipitable Water, above, shows the storm with dry air to the north and west. Tropical cyclones that approach the Arabian peninsula are rare. Those that do approach are invariably weakened as they ingest the dry air that is typically over Arabia. Diagnostics of wind shear also suggest that Chapala is moving towards a more highly sheared environment.

Microwave imagery, below, shows a very intense eye around 0100 UTC on 30 October. After that time, however, the eye becomes less distinct.

Data from the Indian Satellite Kalpana-1 (data courtesy of the Indian Space Research Organization) shows a peak intensity — as measured by the warmest pixel in the eye — occurred around 1015 UTC on 30 October 2015. The warmest brightness temperature warmed 15 K between 1015 UTC and 1345 UTC.

Meteosat-10 viewed the storm as well, and all 11 channels from 0300 to 1500 UTC, including 0600 and 1200 UTC, are shown below. The water vapor channels, in particular, show the very dry air over the Arabian Peninsula. In addition, the animation shows gradual warming of the coldest cloud tops. Data from Meteosat-7, (source) viewing the Indian Ocean, shows the rapid intensification of this small storm. (See also this Meteosat-7 Visible imagery courtesy of the British Met Office).

See also this blog post on this rare event.

Cyclone Gonu in 2007 also affected the Arabian Peninsula (and Iran). The toggle below shows Meteosat-7 imagery of the two storms near their respective peak intensities (Chapala’s intensity plot with time is shown here). Gonu was a far more symmetric storm with more expansive cold clouds tops, but the overall sizes of both storms were similar.

INSAT-3D viewed the storm as well. The near-infrared 0.86 µm imagery, above, highlights the land-sea differences very well as well as showing a compact eye.

A Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image of Cyclone Chapala is shown below.

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Many of the islands in Indonesia have been shrouded in smoke for much of October. RGB composites from Himawari-8, above, for 0200 UTC on each day from 08-26 October 2015 testify to the dense smoke, especially over the island of Borneo. News reports suggest the haze will persist through the end of the year. This is in part due to the strong El Nino event ongoing; El Nino events typically suppress rainfall over the western tropical Pacific basin.

Smoke detection using visible channels, such as those combined in the true color imagery above, is straightforward. At night, however, visible imagery is not available. The animation below shows the difficulty in detecting smoke using infrared imagery. Although parts of the smoke plume show up, the widespread pall of smoke is not captured. Hot spots can be detected using the 3.9 µm (and 2.3 µm) bands on Himawari-8, but viewing the transport of the resultant smoke is a challenge. Except for the VIIRS Day/Night Band imagery from Suomi NPP, then, nighttime smoke detection relies on model output (Source).

The SSEC RealEarth web map server can be used to take a closer look at the islands of Borneo and Sumatra from 20-26 October. Daily comparisons of Suomi NPP VIIRS fire detections and true-color RGB images shown below revealed that although there was a gradual decreasing trend in the number and areal coverage of fires by 26 October, a great deal of smoke still remained over much of the region.

A daily time series plot of weather conditions at the major airport of Kuala Lumpur, below, showed that the surface visibility was often restricted to less than 1 mile during the 20-26 October period.

The Suomi NPP VIIRS instrument contains a day-night sensor that produces useful visible imagery when illuminated by the Moon (and a full Moon occurred on 27 October 2015). The image above from 1837 UTC on 26 October (Courtesy William Straka, SSEC) shows a pall of smoke from Borneo to Sumatra. Thunderstorms are also present over the South China Sea and Borneo. An toggle of the Day Night Band, the 3.9 µm infrared and the 1.6 µm infrared imagery shows that hot spots associated with fires can be detected (enhanced as orange in the 3.9 µm and white in the 1.6 µm), but the associated smoke is mostly undetected in the infrared.

Two sites, one NASA and one NOAA, can give additional information about the smoke. The toggle below, taken from imagery at the NASA site, shows MODIS True-Color imagery, Aeorosol Optical Depth (AOD) (in NASA Worldview, with units) (in cloud-free regions) and retrieved Carbon Monoxide concentrations (in NASA Worldview, with units). AODs are very large, and CO concentrations are off the scale.

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