Typhoon Warnings on Guam for Category 2 Typhoon Dolphin

Typhoon warnings are flying for the U.S. Mariana Islands, including Guam, Rota, Tinian, and Saipan, as Typhoon Dolphin races west-northwest towards the islands at 18 mph. Guam radar shows the outer bands of Dolphin are already affecting the islands, and Guam is under a Flash Flood Watch for rainfall amounts of 8 - 12". Dolphin has intensified only slightly in the past 24 hours; the 8 am EDT Thursday advisory from the Joint Typhoon Warning Center (JTWC) put Dolphin's winds at 110 mph, up from 105 mph 24 hours previous to that, and the Japan Meteorological Agency estimated that the central pressure had held steady at 965 mb. The lack of intensification is due to the fact that wind shear has been in the moderate range, 10 - 20 knots, driving dry air to the west of Dolphin into the circulation. Satellite loops show that Dolphin has shown a slight increase in the intensity and areal coverage of its heavy thunderstorms on Thursday morning, but no eye was apparent. Sea surface temperatures (SSTs) are near 29°C (84°F), and warm waters extend to great depth along Dolphin's track, giving it plenty of heat energy to draw upon for intensification. Dolphin should be able to intensify to Category 3 typhoon status by the time it reaches Guam, but the continued presence of moderate wind shear and dry air should keep the storm below Category 4 strength until after it passes Guam. The latest 00Z Thursday run of the European model and 06Z run of the GFS model show Dolphin passing about 30 - 110 miles to the north of Guam between 06 - 09 UTC Friday (2 am - 5 am U.S. Eastern Daylight Time.) On this track, the island of Rota would receive the worst of Dolphin, and Guam would experience the weaker (left front) side of the typhoon. A strong trough of low pressure should recurve the storm to the north out to sea late this weekend, and Dolphin may pass close enough to Iwo Jima on Tuesday to bring that island typhoon conditions. The GFS model is also advertising that a tropical disturbance near the Equator in the waters southeast of Guam (95W) will organize early next week into a tropical depression, but it is too early to be confident of this prediction.


Figure 1. Latest image from the Guam radar.

The last typhoon on Guam: thirteen years ago
As discussed in detail in yesterday's post, the last typhoon to strike Guam was Typhoon Pongsona, which hit the island as a Category 4 super typhoon with 150 mph winds on December 8, 2002. The last tropical storm to affect Guam was Tropical Storm Saomai of August 2006, which had 50 mph winds when it moved over the island. May is exceptionally early for Guam to be worrying about a typhoon; according to NOAA's Historical Hurricane Tracks website, no typhoon has affected the island in the months of February through June since record keeping began in 1945.

Storm chaser Jim Edds is on Guam, and will be documenting the impact of Dolphin on the island via his Twitter feed.

The NWS in Guam is putting out special advisories and local statements on Dolphin. Wave heights are expected to peak at 22 - 30 feet as the typhoon passes the island.

Bob Henson will have an El Niño post by 2 pm EDT.

Jeff Masters