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)

Super Typhoon Noul in the West Pacific Ocean

May 10th, 2015
Himawari-8 0.64 µm visible channel images (click to play animation)

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

Following a period of rapid intensification, Super Typhoon Noul reached Category 5 strength late in the day on 09 May 2015 (ADT plot) as it slowly approached the northern tip of the Philippine island of Luzon. The Japanese Meteorological Agency (JMA) positioned one of the Himawari-8 rapid-scan “target” areas over the tropical cyclone, providing images at 2.5-minute intervals; 0.5-km resolution 0.64 µm visible (Band 4) images (above; click image to play animation; also available as an MP4 movie file and YouTube Video) showed intricate mesovortices within the eye, as well as gravity waves propagating radially outward from the eyewall region.

Tropical Disturbance off the Southeast US Coast

May 7th, 2015
GOES-13 0.63 µm Visible images (click to play animation)

GOES-13 0.63 µm Visible images (click to play animation)

A disorganized subtropical system (Invest Area 90L) located over the southwest Atlantic to the east of Georgia and north of the Bahamas has the potential to become the first named system of the 2015 Atlantic Tropical Season (if named as a subtropical storm, this would be Ana). Visible imagery, above, shows a low-level swirl that is separated from any convection. However, during the 6 hours of the animation, the low-level swirl moves westward, moving more closely to active convection over the Gulf Stream. [Update, 2100 UTC 7 May: later images in the visible animation, above, showed strong convection developing over the surface circulation; another visible image animation with ship reports can be seen here]

Sea-surface temperatures (link) and wind shear (link) from the CIMSS Tropical Cyclones site show nominal conditions for strengthening.

MetOp-A passed over the southeast United States just after 1500 UTC on 7 May. The ASCAT scatterometer data (below) show a well-defined low-level circulation (with most winds just below tropical storm force) south and east of the deepest convection off the South Carolina/Georgia coasts.

ASCAT_07May2015

ASCAT winds from Metop-A and GOES-13 10.7 µm imagery, both near 1500 UTC on 7 May 2015; Surface observations from Fixed Buoys are also plotted (click to enlarge)

Suomi NPP overflew this system at 0700 UTC on 7 May, and imagery from the VIIRS Day/Night Band gave information that allowed a definitive estimate of the location of a low-level circulation. A comparison of the 0702 imagery, below, and the 1826 UTC imagery, following, shows changes in the organization and vertical structure of the developing system.

ASCAT_07May2015

Suomi NPP 11.45 µm infrared and 0.70 µm DayNight band visible imagery at 0702 UTC on 7 May 2015 (click to enlarge)

ASCAT_07May2015

As above, but at 1826 UTC on 7 May 2015 (click to enlarge)

Suomi NPP 1.61 µm near-infrared imagery can be used during the day to identify cirrus clouds: ice particles absorb (and do not reflect) radiation in these near-infrared wavelengths, but water droplets reflect. Thus, ice clouds appear dark. In the visible, both water and ice clouds are bright. The toggle below shows the 1.61 and the Visible imagery from Suomi-NPP.

ASCAT_07May2015

Suomi NPP 1.61 µm near-infrared and 0.65 µm visible imagery at 1826 UTC on 7 May 2015 (click to enlarge)

At 2006 UTC, the International Space Station’s RapidScat instrument provided surface scatterometer winds (below) that depicted the broad circulation of Invest AL90; the strongest winds were located farther away from the center of the feature.

GOES-13 0.63 µm visible image with an overlay of RapidScat surface scatterometer winds

GOES-13 0.63 µm visible image with an overlay of RapidScat surface scatterometer winds

08 May Update: Invest Area AL90 was upgraded to Subtropical Storm Ana by the National Hurricane Center around 02 UTC. A Terra MODIS 11.0 µm IR image at 0249 UTC is shown below, with overlays of the MSLP analysis, buoy reports, and RTMA surface winds.

Terra MODIS 11.0 µm IR channel image, with MSLP analysis, buoy reports, and RTMA surface wind analysis

Terra MODIS 11.0 µm IR channel image, with MSLP analysis, buoy reports, and RTMA surface wind analysis

A few hours later, a 0643 UTC comparison of Suomi NPP VIIRS 11.45 µm IR and 0.7 µm “visible image at night” Day/Night Band data is shown below.

Suomi NPP VIIRS 11.45 µm IR and 0.7 µm Day/Night Band images

Suomi NPP VIIRS 11.45 µm IR and 0.7 µm Day/Night Band images

For more information on this system, see the National Hurricane Center website.