The long-lasting remnants of Tropical Storm Bill

June 21st, 2015
Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (click to enlarge)

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (click to enlarge)

Advisories on Tropical Storm Bill were initiated when the system organized and intensified off the coast of Texas at 03 UTC on 16 June 2015 (GOES-13 IR image animation). Bill moved inland during the afternoon hours on 16 June, as can be seen in a comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 1916 UTC (above).

Late in the day on 17 June, the general appearance of downgraded Tropical Depression Bill on GOES-13 6.5 µm water vapor channel imagery (below) began to suggest that the system might be undergoing an extratropical transition (intrusion of dry air in the southern quadrant, along with a blosominig comma head signature on the northern quadrant) — but Bill maintained sufficient tropical characteristics to continue being named a tropical depression.

GOES-13 6.5 µm water vapor channel images, with surface pressure and frontal analyses (click to play animation)

GOES-13 6.5 µm water vapor channel images, with surface pressure and frontal analyses (click to play animation)

The circulation of TD Bill maintained its identity on satellite imagery as the storm remained over land for the next 3+ days, curving northeastward and moving across the Ohio River Valley region. Slow-moving TD Bill dropped over 12 inches of rain at some locations in Texas and Oklahoma, with amounts exceeding 8 inches in Missouri and 6 inches in Indiana (WPC storm total rainfall totals), before being designated a post-tropical feature at 21 UTC on 20 June (WPC advisories).

GOES-13 10.7 µm IR channel images (click to play animation)

GOES-13 10.7 µm IR channel images (click to play animation)

The history of Bill can be followed in a multi-day animation of GOES-13 10.7 µm IR channel imagery (above); in addition, the lower-tropospheric circulation of Bill can be followed using the CIMSS 850 hPa relative vorticity product (below).

GOES-13 850 hPa relative vorticity product (click to play animation)

GOES-13 850 hPa relative vorticity product (click to play animation)

As the post-tropical remnants of Bill emerged over the Atlantic Ocean early in the day on 21 June, it still appeared to be associated with an arc of deep convection as seen on a comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 1742 UTC (below). A similar comparison of Terra MODIS visible and IR images at 1514 UTC can be seen here.

Soumi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Soumi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Hurricane Blanca in the eastern Pacific Ocean

June 4th, 2015
Suomi NPP VIIRS Day Night Band 0.70 µm Visible and 11.35 µm infrared imagery over Blanca, 0829 UTC 4 June 2015 (Click to enlarge)

Suomi NPP VIIRS Day Night Band 0.70 µm Visible and 11.35 µm infrared imagery over Blanca, 0829 UTC 4 June 2015 (Click to enlarge)

Suomi NPP overflew Hurricane Blanca early in the morning on 4 June, during a near-full Moon, and the Day Night Band imagery, above, toggled with the 11.35 µm imagery, show the hurricane. (Day/night band imagery of the eye is here, the entire storm is here, and zoomed out is here; click for 11.35 µm imagery of the eye, the entire storm, and zoomed out). Deep convection overnight did not wrap all the way around the storm. Evidence of dry air entrained into the circulation is apparent.

GOES-15 Imager 10.7 µm infrared channel images (click to play animation)

GOES-15 Imager 10.7 µm infrared channel images (click to play animation)

The 3-hourly animation of 10.7 micron imagery, above, from 3-4 June 2015 shows Hurricane Blanca southwest of the Mexican coast, drifting southwestward. Cold cloud tops that were apparent at the start of the loop warm by the end, perhaps because convection is being suppressed by the presence of dry air. MIMIC Total Precipitable Water (below) suggests that dry air is being entrained into Blanca’s circulation from the north. (Update on Andres, also apparent in the MIMIC Total Precipitable Water animation: This overlay of Metop ASCAT winds on top of GOES 10.7 imagery from ~0530 UTC on June 4 shows a swirl that is offset from the convection. Andres is forecast to become post-tropical later on June 4.)

MIMIC Total Precipitable Water animation for the 72 hours ending 1300 UTC on 4 June 2015 (click to enlarge)

MIMIC Total Precipitable Water animation for the 72 hours ending 1300 UTC on 4 June 2015 (click to enlarge)

Visible imagery from GOES-13 from June 3 and June 4, below, show a less distinct/cloudier eye on 4 June compared to 3 June. Multiple overshooting tops persist in the circulation of the system, but the coarse 30-minute temporal resolution of the imagery cannot capture the lifecycle of these quickly evolving events.

GOES-13 Imager 0.63 µm visible channel images (click to play animation)

GOES-13 Imager 0.63 µm visible channel images (click to play animation)

Water vapor imagery from GOES-13 from June and June 4, below, also confirm a consistently less organized storm. The dry air penetrating from the north is apparent in the imagery, but it appears not to have entered into the circulation of the storm, at least not at levels detected by the water vapor channel.

GOES-13 Imager 6.5 µm infrared water vapor channel images (click to play animation)

GOES-13 Imager 6.5 µm infrared water vapor channel images (click to play animation)

Morphed Microwave Imagery (MIMIC) from this website shows the evolution of the central eye structure, below. The eyewall that was much closer to the storm center at the start of the animation has been replaced by a weaker, larger eyewall.

Morphed Microwave Imagery, 48 hours ending 1500 UTC 4 June 2015 (click to enlarge)

Morphed Microwave Imagery, 48 hours ending 1500 UTC 4 June 2015 (click to enlarge)

For more information on this storm, please visit the National Hurricane Center website or the SSEC/CIMSS Tropical Weather website.

Dolphin acquires an eye

May 15th, 2015
Himawari-8 11.22 µm infrared channel images (click to play animation)

Himawari-8 11.22 µm infrared channel images (click to play animation)

Himawari-8 infrared imagery (above, at 2.5-minute time steps and available here as an mp4) shows the development of an eye in Typhoon Dolphin shortly after 1400 UTC when the storm was northwest of Guam. With the subsequent arrival of daylight, mesovortices were clearly seen within the eye on 2.5-minute interval rapid scan visible images (animated gif | mp4 movie file).

About 2 hours prior to eye formation, a Metop satellite overpass allowed the ASCAT instrument to provide surface scatterometer winds of Typhoon Dolphin, overlaid on a MIMIC Total Precipitable Water (TPW) image (below; TPW animation). The maximum TPW values were in the 60-65 mm or 2.4-2.6 inch range, and the highest ASCAT wind value was 68 knots in the eastern eyewall region of the storm.

MIMIC TPW product, with an overlay of Metop ASCAT surface scatterometer winds

MIMIC TPW product, with an overlay of Metop ASCAT surface scatterometer winds

During the preceding daylight hours as Category 2 intensity Typhoon Dolphin was approaching Guam, rapid-scan (2.5-minute interval) 0.5-km resolution Himawari-8 0.64 µm visible channel images (below; click image to play animation; also available as an mp4 movie file) revealed a number of large convective bursts — but no eye was yet apparent. As the center of Dolphin passed between the islands of Guam and Rota, the peak wind gust was 70 knots at Agana, Guam (PGUM) and 92 knots at Anderson Air Force Base, Guam (PGUA).

Himawari-8 0.64 µm visible channel images (click to play animation)

Himawari-8 0.64 µm visible channel images (click to play animation)

Typhoon Dolphin approaches Guam

May 14th, 2015
Himawari-8 11.22 µm infrared channel images (click to play animation)

Himawari-8 11.22 µm infrared channel images (click to play animation)

The animation above (available here as an mp4, and here on YouTube) shows 11.22 µm infrared imagery at 2.5-minute time steps (bottom) and 10-minute time steps (top) from Himawari-8 on 14 May 2015. Category 2 intensity Typhoon Dolphin is approaching Guam, seen at the left edge of both panels in the frame. The 2.5-minute imagery gives a much better indication of the quick rise and decay of overshooting tops (IR brightness temperatures of the storm tops approach -95º C!). A 10-minute time step cannot fully resolve the evolution of these features. The 2.5-minute time step also better captures the divergent flow (and outward-propagating gravity waves) at the top of the central dense overcast. No eye was yet apparent in the infrared imagery, or on DMSP SSMI 85 GHz microwave imagery.

A similar animation from the previous day, 13 May, is shown here: gif, mp4, YouTube. The better organization of the storm on 14 May is readily apparent.

How high are the clouds in the Central Dense Overcast (CDO)? Cloud Heights are available from CLAVR-x (Clouds from AVHRR Extended). Data from Geostationary Satellites are processed and are available to download here. Values from COMS-1 and from MTSAT-2 (displayed with McIDAS-V) suggest maximum cloud heights near 55,500 feet.

The MIMIC Total Precipitable Water (TPW) product, below, showed that Typhoon Dolphin was able to tap rich moisture from the Intertropical Convergence Zone (ITCZ) during the 13-14 May period; TPW values within the tropical cyclone circulation were often in the 60-65 mm or 2.5-2.6 inch range (darker red color enhancement).

MIMIC Total Preciptable Water product (click to play animation)

MIMIC Total Preciptable Water product (click to play animation)

Visible Imagery from Himawari-8, just after sunrise on 15 May, show continuous development of short-lived overshooting tops to the east of Guam. More information on the storm is available at the CIMSS Tropical Cyclones site, the JMA Tropical Cyclone site and the Joint Typhoon Warning Center.

Himawari-8 0.6363 µm visible channel images (click to play animation)

Himawari-8 0.6363 µm visible channel images (click to play animation)