Flooding Rains in southern California

July 20th, 2015
GOES-15 Infrared Water Vapor (6.5 µm) Images  (click to play animation)

GOES-15 Infrared Water Vapor (6.5 µm) Images (click to play animation)

Unusual rains causing flooding and mudslides hit southern California (San Diego in particular) on 18-19 July 2015. The two-day rain total (1.69″) at Lindbergh Field broke the monthly record for July (previous record, 1.29″) and exceeded the January-April 2015 rainfall (the typical wet season) at the station. The San Diego Padres had their first July rainout ever, and the Anaheim Angels had their first rainout since 1995! What caused the rains? The water vapor imagery, above, shows the three systems that contributed. Pacific Hurricane Dolores (Track) was declared post-tropical off the coast of Baja California at 0300 UTC on 19 July. Farther to the west, Pacific Tropical Storm Enrique was declared post-tropical at 0300 on 18 July. High pressure aloft was helping support a Gulf Surge, a surge of moisture up the Gulf of California towards the desert southwest. Two animations of MIMIC Total Precipitable Water, below, show the surge and also show that moisture associated with main circulation of Dolores remains mostly offshore until late on the 19th, after the heavy rains had ended.

MIMIC Total Precipitable Water, 0000 UTC on 15 July through 0000 UTC on 18 July 2015 (click to enlarge)

MIMIC Total Precipitable Water, 0000 UTC on 15 July through 0000 UTC on 18 July 2015 (click to enlarge)

MIMIC Total Precipitable Water, 0000 UTC on 18 July through 0000 UTC on 21 July 2015  (click to enlarge)

MIMIC Total Precipitable Water, 0000 UTC on 18 July through 0000 UTC on 21 July 2015 (click to enlarge)

The Blended Precipitable Water Product (data collected from this site), below, also shows evidence of a Gulf Surge of moisture moving northward through the Gulf of California in the few days preceding the rains.

NESDIS Blended Total Precipitable Water (left) and Percent of Normal (right), 1200 UTC on 15 July through 1200 UTC on 20 July 2015 (click to animate)

NESDIS Blended Total Precipitable Water (left) and Percent of Normal (right), 1200 UTC on 15 July through 1200 UTC on 20 July 2015 (click to animate)

The animation of 10.7 µm imagery, below, suggests that the precipitation on Saturday the 18th was associated more with the Gulf Surge of moisture (which surge was likely influenced both by the large scale synoptic flow and by the circulation of Dolores); precipitation on Sunday the 19th seems more directly influenced by Dolores.

GOES-15 Infrared (10.7 µm) Images  (click to play animation)

GOES-15 Infrared (10.7 µm) Images (click to play animation)

What part did the upper-level outflow jets from the two tropical cyclones play in this event? Consider the water vapor animation below, zoomed in from the larger-scale view at the top of this post. Outflow from Enrique moves from the southwest part of the domain towards the southern California coast (the low-level circulation of Enrique are at the southwest edge of the domain), moving inland as convection develops on Saturday 18 July 2015. The Total Precipitable Water imagery suggests that convection starts as the leading edge of the Gulf Surge arrives; water vapor imagery suggests a tie to Enrique.

GOES-15 Infrared Water Vapor (6.5 µm) Images  (click to play animation)

GOES-15 Infrared Water Vapor (6.5 µm) Images (click to play animation)

GOES-15 Visible Imagery, below, from Saturday the 18th and from Saturday the 19th suggest rain on 19 July was more directly tied to the circulation of Dolores. On both days, the convective nature of the precipitation is apparent, with numerous overshooting tops present. Convection on Sunday the 19th started over higher terrain first, and then was joined by tropical convection moving in from the ocean.

GOES-15 Visible (0.65 µm) Images, 1300 UTC 18 July through 0300 UTC 19 July 2015  (click to play animation)

GOES-15 Visible (0.65 µm) Images (click to play animation)

GOES-15 Visible (0.65 µm) Images, 1300 UTC 19 July through 0300 UTC 20 July 2015  (click to play animation)

GOES-15 Visible (0.65 µm) Images (click to play animation)

As might be expected, the San Diego sounding (source) shows deep tropical moisture late on the 18th and late on the 19th as the heavy rains occurred. The precipitable water value of 2.10″ at 0000 UTC on 20 July was a top 5 value for July (Source). The rains caused two spikes in the flow of the San Diego River (Link, courtesy Alex Tardy, NWS San Diego).

Stuve plots of radiosonde data at 72293, 0000 and 1200 UTC 19 July and 0000 UTC 20 July 2015  (click to enlarge)

Stuve plots of radiosonde data at 72293, 0000 and 1200 UTC 19 July and 0000 UTC 20 July 2015 (click to enlarge)

The convection over San Diego produced many lightning strikes on Saturday, as shown on the map below, courtesy of Alex Tardy, NWS San Diego.

Lightning Strikes for the 24 hours ending 2 PM PDT on Saturday 18 July 2015 (click to enlarge)

Lightning Strikes for the 24 hours ending 2 PM PDT on Saturday 18 July 2015 (click to enlarge)

Unusual Double Eyewall structure in Himawari-8 Infrared Imagery of Typhoon Nangka

July 13th, 2015
Himawari-8 10.35 µm infrared imagery, 0540-1540 UTC on 13 July 2015 (Click to animate)

Himawari-8 10.35 µm infrared imagery, 0540-1540 UTC on 13 July 2015 (click to animate)

Himawari-8 10.35 µm infrared imagery showed an unusual (for infrared imagery) double-eyewall structure in Typhoon Nangka over the western Pacific Ocean on 13 July 2015. For such a feature to appear in infrared imagery, the secondary circulations of both the inner and outer eyewall need to be intense enough to support the downdraft/cloud-clearing necessary to create the “moats” between them. Microwave imagery of the storm, below, viewed via MIMIC (from this site), also showed the double eyewall structure quite well. This double-eyewall signature typically indicates that a tropical cyclone is experiencing an eyewall replacement cycle (ERC), which signals that a (temporary) decrease in intensity is soon to follow.

MIMIC imagery of Typhoon Nangka, 0000 - 1200 UTC on 13 July 2015 (Click to enlarge)

MIMIC imagery of Typhoon Nangka, 0000 – 1200 UTC on 13 July 2015 (click to enlarge)

Several hours later, a DMSP SSMIS 85 GHz microwave image at 1756 UTC, below, indicated that the ERC was essentially complete. Subsequently, the Joint Typhoon Warning Center slightly downgraded the intensity of Typhoon Nangka for their 21 UTC advisory. While not as well-defined as in the Himawari-8 imagery, the double-eyewall signature was still evident in the lower-resolution (4-km, vs  2-km) MTSAT-2 IR imagery (animation).

DMSP SSMIS 85 GHz microwave image and MTSAT-2 10.8 µm Infrared image (click to enlarge)

DMSP SSMIS 85 GHz microwave image and MTSAT-2 10.8 µm Infrared image (click to enlarge)

The Himawari-8 Target Sector was centered over Typhoon Nangka during this time; an IR image animation with a 2.5-minute timestep, below (courtesy of William Straka, SSEC), showed the evolution of the double eyewall signature, along with 2 pulses of storm-top gravity waves which propagated radially outward away from the center in the northern semicircle of the typhoon.

Himawari-8 10.4 µm IR channel images (click to animate large 115-Megabyte file)

Himawari-8 10.4 µm IR channel images (click to animate large 115-Megabyte file)

Chan-Hom approaches the coast of China

July 10th, 2015


The video above shows 5 hours of Himawari-8 10.35 µm Infrared imagery from Typhoon Chan-Hom as it moves through the Yellow Sea towards the coast of China (original animated gif here; mp4 here). The location of Shanghai is indicated in the first frame, and this blog post talks about the history of typhoon landfalls near Shanghai. The appearance of the storm in the animation above is relatively constant.

Himawari-8 10.35 µm infrared imagery, 1447-2002 UTC on 6 July 2015 (Click to animate)

Himawari-8 6.2 µm (top), 6.9 µm (middle) and 7.3 µm (bottom) water vapor infrared imagery, 0000 UTC 8 July 2015 – 1500 UTC 10 July 2015 (click to animate)

The three water vapor channels from Himawari-8, above, over the course of the past 3 days show a steady northwestward motion and a decrease in the cold cloud tops surrounding the storm, consistent with the weakening that has been observed after peak intensity at ~1500 UTC on July 9. Typhoon Nangka remains southeast of Chan-Hom; Typhoon Linfa has dissipated after having made landfall over south China. Chan-Hom’s path (below) is over progressively colder water and significant intensification is not expected before landfall.

Sea-Surface Temperatures over the Yellow Sea, along with Chan-Hom's past and projected path (Click to enlarge)

Sea-Surface Temperatures over the Yellow Sea, along with Chan-Hom’s past and projected path (click to enlarge)

A DMSP SSMIS 85 GHz microwave image at 0946 UTC on 10 July, below, showed that Category 3 Typhoon Chan-Hom was undergoing an eyewall replacement cycle as the small inner eyewall was being replaced by a much larger outer eyewall. Also on the image are 1244 UTC Metop ASCAT surface scatterometer winds, which displayed a large area with winds in the 50-59.9 knot range along the western periphery of the tropical cyclone.

DMSP SSMIS microwave image at 0946 UTC, and Metop ASCAT winds at 1244 UTC (click to enlarge)

DMSP SSMIS microwave image at 0946 UTC, and Metop ASCAT winds at 1244 UTC (click to enlarge)

Tropical Storm Ela east of Hawai’i

July 9th, 2015
Suomi NPP VIIRS visible (0.64 µm) and Infrared (11.45 µm) images of Tropical Depression 4E at 2224 UTC on 08 July

Suomi NPP VIIRS visible (0.64 µm) and Infrared (11.45 µm) images of Tropical Depression 4E at 2224 UTC on 08 July

Tropical Storm Ela began as Tropical Depression 4E about 900 miles east of Hilo, Hawai’i around 03 UTC on 08 July 2015. A comparison of daytime images of Suomi NPP VIIRS 0.64 µm Visible channel and 11.45 µm Infrared channel images (above) showed the somewhat disorganized appearance of TD 4E at 2224 UTC on 08 July — the low-level circulation center (LLCC) was located to the southwest of the clusters of deep convection associated with the system.

About 12 hours later, a nighttime comparison of VIIRS 0.7 µm Day/Night Band (DNB) and 11.45 µm Infrared channel images at 1052 UTC on 09 July (below) continued to show a similar disconnect between the LLCC and clusters of deep convection in the eastern semicircle of recently-upgraded Tropical Storm Ela. The coldest cloud-top IR brightness temperature in the convection closest to the storm center was -78º C. Even though the Moon was in the Waning Crescent phase (at 43% of Full), it still provided enough illumination to aid in the location of the LLCC, as noted in a discussion issued by the CPHC:

TROPICAL STORM ELA DISCUSSION NUMBER   7
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP042015
500 AM HST THU JUL 09 2015

A 1052Z VIIRS DAY/NIGHT BAND IMAGE WAS INSTRUMENTAL IN HELPING TO LOCATE THE PARTIALLY EXPOSED CENTER OF ELA THIS MORNING.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared (11.45 µm) images of Tropical Storm Ela at 1052 UTC on 09 July

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared (11.45 µm) images of Tropical Storm Ela at 1052 UTC on 09 July

According to satellite-derived winds products from the CIMSS Tropical Cyclones site, there was strong divergence and a well-defined outflow channel in the northern quadrant of Ela (below), whose center was located at 19.3º N 145.1º W at 09 UTC on 09 July.

GOES-15 water vapor (6.5 µm) images with satellite wind derived upper tropospheric divergence and winds

GOES-15 water vapor (6.5 µm) images with satellite wind derived upper tropospheric divergence and winds

The reason that the LLCC remained exposed from the elements of deep convection was the fact that Ela was encountering increasing amounts of southwesterly deep-layer wind shear as it tracked northwestward  (below).

GOES-15 Infrared (10.7 µm) images, with an overlay of deep-layer wind shear at 18 UTC on 09 July

GOES-15 Infrared (10.7 µm) images, with an overlay of deep-layer wind shear at 18 UTC on 09 July

========================= Added July 10 2015 ============================

The southwesterly shear over the storm decoupled the surface circulation from the overlying convection, and Ela was downgraded to a depression early on 10 July 2015. The 0700 UTC 10 July 2015 image below shows ASCAT Scatterometer winds depicting a low-level swirl well east of Hawai’i; deep convection with the system is hundreds of kilometers to the northeast.

ASCAT Scatterometer winds and GOES-15 infrared (10.7 µm) imagery, 0700 UTC 10 July 2015

ASCAT Scatterometer winds and GOES-15 infrared (10.7 µm) imagery, 0700 UTC 10 July 2015 (Click to enlarge)