Rosa became a Tropical Storm on 25 September 2018, and reached peak intensity as a Category 4 Hurricane on 28 September. As it gradually weakened and made landfall over Baja California on 02 October, its moisture moved across the US Desert Southwest causing heavy rainfall and flash flooding — parts of Arizona received record-setting rainfall (NWS Phoenix | NWS Flagstaff), with precipitation rates as high as 1 inch in 30 minutes in the Phoenix area. GOES-16 (GOES-East) “Clean” Infrared Window (10.3 µm) images during the 8 days from 25 September to 02 October (above) showed the life cycle of Rosa.

A closer look at Rosa during that same time period is shown below. The image interval is 15 minutes, except for 5-minute imagery during a test of Mode 4 scanning strategy on 01 October (from 0000-1550 UTC).

The transport of tropical moisture associated with Rosa could be followed using the MIMIC Total Precipitable Water product (below). The moisture over southwestern Arizona on 02 October was >4 standard deviations above normal for that region and time of year.

The increase in deep tropical moisture was very evident in plots of rawinsonde data from Tucson, Arizona (below) — Total Precipitable Water peaked at 43.9 mm or 1.73 inches at 12 UTC on 01 October.

Here's a look at the rainfall totals over the past 48 hours across the southern half of Arizona. Impressive totals across western Pima county and far southern Maricopa county. #azwx pic.twitter.com/hi7A54DHhM

— NWS Tucson (@NWSTucson) October 2, 2018

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GOES-15 (GOES-West) Infrared Window (10.7 µm) images (above) showed the formation of a well-defined eye of Hurricane Walaka during a period of rapid intensification (ADT | SATCON) from 0000-2330 UTC on 01 October 2018; Walaka was classified a Category 5 hurricane as of the 02 October 00 UTC advisory. Walaka was moving over very warm water with Sea Surface Temperatures of 30ºC.

A 1536 UTC DMSP-16 SSMIS Microwave (85 GHz) image from the CIMSS Tropical Cyclones site (below) revealed a small eye (reported to be 20 nautical miles in diameter at 21 UTC).

A side-by-side comparison of JMA Himawari-8 and GOES-15 Infrared Window images (below) showed Walaka from 2 different satellite perspectives — the superior spatial resolution of Himawari-8 (2 km, vs 4 km for GOES-15) was offset by the much larger viewing angle. Cloud-top infrared brightness temperatures were -80ºC and colder (shades of violet) from both satellites early in the animation, but warmed somewhat into the -70 to -75ºC range by 00 UTC on 02 October.

===== 02 October Update =====

Walaka remained classified as a Category 5 hurricane until the 15 UTC advisory on 02 October, when it was assigned Category 4 status after some weakening as a result of an overnight eyewall replacement cycle. A toggle between NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images (above; courtesy of William Straka, CIMSS) showed the storm at 1240 UTC or 2:40 am local time.

GOES-15 Infrared Window (10.7 µm) images (below) showed the northward motion of Waleka. Given that the storm was forecast to pass very close to Johnston Atoll, the US Coast Guard was dispatched to evacuate personnel on Johnston Island.

The MIMIC-TC product (below) showed the eyewall replacement cycle during the 0000-1445 UTC period.

Around 1830 UTC, a toggle between GOES-15 Infrared (10.7 µm) and GPM GMI Microwave (85 GHz) images (below) showed a small eye, with evidence of a larger outer eyewall suggesting that another eyewall replacement cycle was taking place.

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GOES-17 Data shown in this post are preliminary and non-operational.

Continuous Full Disk (Mode 4) Testing is occurring on October 1 2018.   Mode 4 is the highest data flow rate for the ABI and results in a Full Disk image every 5 minutes.  No mesoscale sectors are produced during Mode 4 operations.  Five-minute CONUS imagery can be produced by subsecting the 5-minute Full-Disk Imagery.  This testing started at 0000 UTC on 1 October and will end at 0000 UTC on 2 October.

The animation above shows GOES-17 Full-Disk imagery for the upper-level water vapor imagery (6.19 µm) with a 5-minute cadence.  The GOES-16 animation for the same time and location is below.

Careful inspection of the imagery from the two satellites might reveal differences in brightness temperatures between the two instruments. This difference is due to view-angle differences. When the satellite is scanning near the limb, computed brightness temperatures will be cooler because more information detected by the satellite comes from the upper part of the atmosphere. Compare, for example, brightness temperatures just west of former Pacific Hurricane Rosa just west of Baja California. GOES-17, at 89.5 W Longitude, sees warmer temperatures than GOES-16 at 75.2 W Longitude. GOES-16’s view is more oblique, and is through more of the colder upper atmosphere.

(Update: GOES-16 returned to Mode-3 scanning at 1549 UTC on 1 October. Continuous Full Disk scanning on GOES-16 lead to degradation of derived products).

Update #2: Animations of 5-minute Full Disk GOES-17 Mid-level Water Vapor (6.9 µm) and “Red” Visible (0.64 µm) images from 0000-2355 UTC on 01 October are shown below.

One interesting feature on GOES-17 Visible imagery was the east-to-west progression of sun glint off the water of the Amazon River and its tributaries, beginning near the mouth of the river in northeastern Brazil and ending in Ecuador (below).

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Medicane “Zorbas” — as named by Freie Universität Berlin (surface analyses) — developed in the Mediterranean Sea late in the day on 27 September 2018. A toggle between VIIRS Day/Night Band (0.7 µm) images from NOAA-20 and Suomi NPP (above; courtesy of William Straka, CIMSS) revealed the well-defined circulation of the storm a few hours after Midnight local time on 28 September. Note the bright streak north of the storm center on the NOAA-20 image — this was an area of clouds illuminated by intense lightning activity. Other less prominent lightning streaks were evident in thunderstorms farther to the east over the Mediterranean Sea. On the Suomi NPP image, a small bright spot could be seen, evidence of minor volcanic activity at Mount Etna on the island of Sicily, as well as the hazy signature of a plume of blowing dust/sand that was moving northward off the coast of Libya. The corresponding VIIRS Infrared images are available here.

During the following daylight hours of 28 September, EUMETSAT Meteosat-11 High Resolution Visible (0.8 µm) images (below) showed the storm as it became better organized and increased intensity. Another dense plume of blowing dust/sand began to move off the coast of Libya late in the day.

On 29 September, Meteosat-11 Visible (0.8 µm) images (below) showed the Medicane moving inland along the Peloponnese coast of southern Greece — shortly after the storm center passed, winds gusted to 48 knots at Kalamata at 1220 UTC (while a heavy thunderstorm was being reported).

A sequence of Terra and Aqua MODIS True Color Red-Green-Blue (RGB) images from 28 and 29 September from RealEarth (below) showed another view of the Zorbas on those 2 days (the valid time of the Terra MODIS image showing the eye-like feature on 29 September was 0911 UTC). Sea Surface Temperatures were near 25ºC in the central Mediterranean Sea where Zorbas was intensifying.

Hourly images of the MIMIC Total Precipitable Water product (below) showed moisture associated with the storm, which produced heavy rainfall and flash flooding in parts of southern Greece — the NESDIS Blended TPW Anomaly product indicated that this moisture was as much as 200% of normal for the region and date. Additional information and videos can be found here.

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