Tropical cyclones « CIMSS Satellite Blog

Tropical Storm Iba off the coast of Brazil

March 24th, 2019 | Scott Bachmeier

GOES-16 “Red” Visible (0.64 µm) images, with GLM Groups plotted in red [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) and “Clean” Infrared Window (10.3 µm) images (below) showed the formation of Tropical Storm Iba off the east coast of Brazil at 16 UTC on 24 March 2019 (surface analyses). Plots of GLM Groups revealed some intermittent lightning activity. Tropical cyclones in the South Atlantic basin are rare — the last was in 2010, and only one example (Catarina in March 2004) is known to have reached hurricane intensity.

GOES-16 “Clean” Infrared Window (10.3 µm) images [click to play animation | MP4]

A toggle between NOAA-20 VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) from RealEarth (below) showed Iba at 1610 UTC.

NOAA-20 VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images at 1610 UTC [click to enlarge]

GOES-16 Infrared images with an overlay of deep-layer wind shear valid at 18 UTC from the CIMSS Tropical Cyclones site (below) revealed a very tight gradient of shear over Iba. However, the shear gradient began to relax somewhat by 21 UTC.

GOES-16 “Clean” Infrared Window (10.3 µm) images, with an overlay of 18 UTC deep-layer wind shear [click to enlarge]

In a sequence of GOES-16 “Clean” Infrared Window (10.3 µm) and Infrared-Water Vapor (10.3-6.9µm) brightness temperature difference (BTD) images (below), the clusters of deep convection propagating southward — east of Iba’s center of circulation, denoted by “I” — exhibited large negative BTD values (darker shades of red) suggestive of significant cloud-top penetration into the lower stratosphere (reference).

GOES-16 “Clean” Infrared Window (10.3 µm) and Infrared-Water Vapor (10.3-6.9µm) BTD images [click to enlarge]

GOES-16 Visible images with an overlay of 1138 UTC ASCAT surface scatterometer winds from the Metop-A satellite (below) showed speeds in the 40-49 knot range (yellow barbs).

GOES-16 “Red” Visible (0.64 µm) images, with Metop-A ASCAT winds at 1137 UTC [click to enlarge]

The MIMIC Total Precipitable Water product (below) showed that Iba was embedded within a plume of moisture that extended southeastward off the coast of Brazil.

MIMIC Total Precipitable Water product [click to play animation]

Sea Surface Temperature values (below) were around 30ºC in the waters where Iba intensified.

Sea Surface Temperature analysis at 2230 UTC on 23 March [click to enlarge]

===== 25 March Update =====

GOES-16 “Red” Visible (0.64 µm) with GLM Groups (left) and “Clean” Infrared Window (10.3 µm, right) images [click to play animation | MP4]

A comparison of GOES-16 Visible and Infrared images (above) showed that increasing deep-layer wind shear had exposed the low-level circulation center of Iba. However, GLM Groups plotted on the Visible images revealed an increasing amount of lightning activity associated with a convective burst that began to wrap around the southern edge of the storm center after 15 UTC — and a brief cloud-top infrared brightness temperature of -90ºC (yellow pixel embedded with darker purple shades) was seen at 1635 UTC.

A timely overpass of the Suomi NPP satellite at 1639 UTC provided 375-meter resolution VIIRS True Color RGB and Infrared Window (11.45 µm) images (below), which showed a large overshooting top that exhibited infrared brightness temperatures of -90ºC and colder (yellow), with a warmer ring of compensating subsidence immediately surrounding it. The coldest pixel had a brightness temperature of -103.7ºC — which is almost 1ºC colder than the -102.96ºC value noted over Australia in 2008.

Suomi NPP VIIRS True Color RGB and Infrared Window (11.45 µm) images [click to enlarge]

The explosive growth of that convective burst was very apparent in a toggle between VIIRS Infrared images from NOAA-20 at 1549 UTC and Suomi NPP at 1639 UTC (below, courtesy of William Straka, CIMSS). Note that the images use a slightly different variant of the color enhancement. A comparison of VIIRS True Color and Infrared images from NOAA-20 and Suomi NPP viewed using RealEarth is available here.

VIIRS Infrared (11.45 µm) images from NOAA-20 at 1549 UTC and Suomi NPP at 1639 UTC [click to enlarge]

Posted in GLM, GOES-16, Lightning, Metop, Microwave, NOAA-20, RealEarth, Red-Green-Blue (RGB) images, Satellite winds, Suomi NPP, Tropical cyclones, VIIRS | No Comments »

Tropical Cyclone Veronica north of Australia

March 21st, 2019 | Scott Bachmeier

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 1716 UTC [click to enlarge]

A toggle between Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images (above) showed Category 4 Cyclone Veronica off the northern coast of Western Australia at 1716 UTC on 21 March 2019. Ample illumination from a Full Moon maximized the “visible image at night” capability of the Day/Night Band.

In a comparison of Microwave images from Suomi NPP ATMS at 1716 UTC and from GCOM-W1 AMSR2 at 1732 UTC (below), an eyewall that was nearly completely closed was apparent. Suomi NPP and GCOM-W1 images courtesy of William Straka, CIMSS.

Microwave images from Suomi NPP ATMS at 1716 UTC and from GCOM-W1 AMSR2 at 1732 UTC [click to enlarge]

A DMSP-17 SSMIS Microwave (85 GHz) image at 2246 UTC from the CIMSS Tropical Cyclones site is shown below. The deep-layer Wind Shear at 21 UTC was low (green contours), and Sea Surface Temperature values were quite high — both factors favorable for continued intensification as Veronica moved slowly toward the coast.

DMSP-17 SSMIS Microwave (85 GHz) image at 2246 UTC, with an overlay of 21 UTC deep-layer Wind Shear, and Sea Surface Temperature [click to enlarge]

2.5-minute interval rapid scan Himawari-8 Infrared Window (10.4 µm) images (below) showed increasing organization to the eyewall structure. At times the cloud-top infrared brightness temperatures were -90ºC and colder (yellow pixels embedded within darker purple). Note: the rapid scan sector was re-poositioned eastward at 0100 UTC (to monitor Cyclone Trevor), so 10-minute imaging resumed after that time.

Himawari-8 Infrared Window (10.4 µm) images [click to play animation | MP4]

After sunrise, rapid scan Himawari-8 “Red” Visible (0.64 µm) images (below) revealed that the large eye was completely cloud-filled.

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

Posted in DMSP, GCOM-W1, Himawari-8, Microwave, Satellite winds, Suomi NPP, Tropical cyclones, VIIRS | No Comments »

Cyclone Idai makes landfall in Mozambique

March 14th, 2019 | Scott Bachmeier

Meteosat-8 Infrared (10.8 µm) and DMSP-17 SSMIS Microwave (85 GHz) images of Cyclone Idai at 1630 UTC [click to enlarge]

Meteosat-8 Infrared Window (10.8 µm) and DMSP-17 SSMIS Microwave (85 GHz) images of Cyclone Idai at 1630 UTC [click to enlarge]

Cyclone Idai — which had been slowly intensifying over warm water within the Mozambique Channel since 09 March — made landfall as a Category 2 storm along the coast of Mozambique on 14 March 2019 (storm track). A toggle between Meteosat-8 Infrared Window (10.8 µm) and DMSP-17 SSMIS Microwave (85 GHz) images from the CIMSS Tropical Cyclones site (above) revealed a large and well-defined eye and eyewall structure at 1630 UTC. Idai had been rated at Category 3 intensity during 3 periods of time during its life cycle, most recently at 12 UTC on the day of landfall.

At 1911 UTC, Metop-A ASCAT winds in excess of 60 knots were sampled just west of the eyewall region (below).

Meteosat-8 Infrared Window (10.8 µm) image, with plots of Metop-A ASCAT winds at 1911 UTC [click to enlarge]

A comparison of VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP, visualized using RealEarth, is shown below.

NOAA-20 and Suomi NPP VIIRS True Color RGB and Infrared Window (11.45 µm) images [click to enlarge]

Idai had been moving through an environment of very low deep-layer wind shear — a favorable factor for maintaining its intensity — as shown in an animation of Meteosat-8 Infrared Window (10.8 µm) images (below).

Meteosat-8 Infrared Window (10.8 µm) images with contours of satellite-derived Deep-Layer Wind Shear valid at 18 UTC [click to enlarge]

The MIMIC TC product (below) suggested that Idai might have been in the early stage of an eyewall replacement cycle (ERC) just prior to making landfall. This, after completing a separate ERC during the preceding 48 hours.

MIMIC TC morphed microwave imagery [click to enlarge]

MIMIC TC morphed microwave image product [click to enlarge]

The eye of Idal was becoming cloud-filled as it approached the Mozambique coast, as seen on EUMETSAT Meteosat-8 High Resolution Visible (0.8 µm) images (below).

Meteosat-8 High Resolution Visible (0.8 µm) images [click to play animation]

A time series of surface data from the port city of Beira FQBR (below) showed deteriorating conditions before observations ceased at 15 UTC.

Surface observation data from Beira, Mozambique [click to enlarge]

Incidentally, an overpass of the Landsat-8 satellite on 11 March provided a 30-meter resolution view of the eye (below), soon after Idai’s first period of rapid intensification to Category 3 strength (SATCON). Surface mesovortices were apparent within the eye.

Landsat-8 False Color image of the eye of Idai on 11 March [click to play a zooming animation]

Flooding from Idai led to hundreds of fatalities in Mozambique and Zimbabwe.

Flooded areas near Beira on 19 Mar 2019 computed from #Sentinel1 #MozambiqueFloods @CopernicusEMS @CopernicusEU pic.twitter.com/2OdE6Ixzig

— Simon Gascoin (@sgascoin) March 20, 2019

Posted in DMSP, Landsat, Meteosat, Microwave, NOAA-20, RealEarth, Red-Green-Blue (RGB) images, Suomi NPP, Tropical cyclones, VIIRS | No Comments »

Standing wave west of Tropical Cyclone Pola in the South Pacific

February 26th, 2019 | Scott Bachmeier

Himawari-8 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play animation | MP4]

Himawari-8 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) revealed an interesting standing wave west/northwest of Tropical Cyclone Pola in the South Pacific Ocean on 26 February 2019. The long-lived wave first became apparent just before 0800 UTC, and persisted until about 2330 UTC.

The standing wave feature was also apparent in Himawari-8 “Clean” Infrared Window (10.4 µm) images (below). The abrupt warming of cloud-top infrared brightness temperatures associated with the wave suggests that subsidence was lowering the cloud height. Also note the very cold cloud-top temperatures of -90ºC and colder (yellow pixels embedded within the darker purple enhancement) — this was colder than the tropopause temperature on 12 UTC rawinsonde data from both Nadi, Fiji (NFFN) to the southwest and Pago Pago, American Samoa (NSTU) to the northeast (the wave feature was located closer to the Nadi sounding).

Himawari-8 “Clean” Infrared Window (10.4 µm) images [click to play animation | MP4]

Consecutive VIIRS Infrared Window (11.45 µm) images from Suomi NPP and NOAA-20, as viewed using RealEarth (below) showed a definitive bore-like structure with the wave, especially along the northern end.

VIIRS Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP [click to enlarge]

Himawari-8 “Red” Visible (0.64 µm) images (below) showed the feature during daylight hours — a distinct shadow was being cast during local sunrise, which indicated a sharp drop-off in cloud height from east to west along the wave.

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

A HWRF-P model sounding for the latitude/longitude point 15.42ºS/179.75ºW valid at 18 UTC (source) showed directional wind shear at the 450 hPa pressure level — such a wind shear could have acted to initiate a horizontal roll circulation, creating a narrow zone of cloud-eroding subsidence. In addition, a sharp change in wind direction was seen above 150 hPa on the Paga Pago sounding — and the Nadi sounding showed speed shear with height — which also could have induced a horizontal roll circulation within the upper troposphere.

HWRF-P model sounding for the location 15.42ºS/179.75ºW at 18 UTC [click to enlarge]

An interesting phenomenon was the apparent “shedding” of high-altitude cloud material from the higher/colder cloud canopy of Pola immediately east of the wave feature, as seen in Himawari-8 Shortwave Infrared (3.9 µm) images (below). The westward direction and velocity of this cloud material motion had good agreement with GFS model winds at 150 hPa. Note that this shed cloud material appeared warmer (darker gray) in the 3.9 µm imagery — the shearing of cirrus cloud may have acted to fracture the ice crystals, making them smaller in size and therefore more efficient reflectors of incoming solar radiation.

Himawari-8 Shortwave Infrared (3.9 µm) images, with plots of GFS 150 hPa winds [click to play animation | MP4]

A toggle between GOES-17 (GOES-West) Infrared and Water Vapor images from the CIMSS Tropical Cyclones site (below) showed that the feature was aligned with a couplet of low-level convergence and upper-level divergence at 15 UTC — such an environment could also support a vertically-propagating gravity wave.