Typhoon Dolphin Intensifying as it Heads Towards Guam

Typhoon Dolphin is gathering strength in the waters to the east of the U.S. Mariana Islands, and is a serious threat to strike Guam and the nearby islands as a major typhoon on Friday morning (U.S. EDT.) The 8 am EDT Wednesday advisory from the Joint Typhoon Warning Center (JTWC) put Dolphin's winds at 105 mph, and the Japan Meteorological Agency estimated a central pressure of 965 mb. The latest 00Z Wednesday run of the European model and 06Z run of the GFS model show Dolphin passing within 50 miles of Guam between 06 - 09 UTC Friday (2 am - 5 am U.S. Eastern Daylight Time.) Satellite loops show that Dolphin significantly increased in organization on Wednesday morning, with an increase in the intensity and areal coverage of its heavy thunderstorms and formation of an eye. 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. Wind shear has risen over the past day to the moderate range, 10 - 20 knots, and is expected to remain low to moderate through Friday. Dolphin should be able to intensify to Category 3 typhoon status by the time it reaches Guam, and may rapidly intensify, potentially affecting Guam as a Category 4 super typhoon. Guam will likely be the last land area Dolphin will affect, as a strong trough of low pressure should recurve the storm to the north out to sea late this weekend. 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. Typhoon Dolphin as seen by the MODIS instrument on NASA's Aqua satellite at approximately 03 UTC May 13, 2015. At the time, Dolphin had sustained winds of 85 mph, and a "pinhole" eye with a diameter of only six miles. Image credit: NASA Worldview.

The last typhoon on Guam: thirteen years ago
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. Sustained winds of 144 mph with gusts to 173 mph were recorded on the island, and Andersen Air Force Base was in the eye for two hours. The lowest pressure on Guam was 935 millibars, making Pongsona the third most intense typhoon to strike the island (the others: a 1900 typhoon with a 926 mb pressure, and Typhoon Karen of 1962, at 932 mb). With strong building standards and experience from repeated typhoon strikes (six typhoons in the previous ten years), there was one death from flying glass, and 193 injuries. Damage was over $700 million (2002 US$, $918 million 2015 USD), making Pongsona among the five costliest typhoons on the island. The typhoon also caused heavy damage on Rota and elsewhere in the Northern Mariana Islands, and as a result of its impact, the name Pongsona was retired. 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.


Figure 2. Super Typhoon Pongsona as seen on December 8, 2002. At the time, Pongsona was at its peak strength--Category 4 with 150 mph winds. The image shows Pongsona over the Northern Mariana Islands in the western Pacific Ocean approaching Guam. Image credit: Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC - http://visibleearth.nasa.gov/view_rec.php?id=4761

A record early start to typhoon season
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 (one January storm, Typhoon Roy of 1988, did pass near Guam in January, though.) Guam's early typhoon worries this year reflect how crazy-busy the early part of the 2015 typhoon season has been. The Japan Meteorological Agency (JMA) gave Tropical Storm Dolphin its name on May 9. According to statistics from the Japan Meteorological Agency's database from 1951 - 2015 maintained by Digital Typhoon, this was the earliest appearance on record of the Northwest Pacific's seventh named storm of the year. The previous record was May 19, 1971 (Carla.) Usually by this time of year, just two named storms have appeared; the seventh storm of the year typically doesn't form until the third week of July. According to Colorado State University hurricane scientist Phil Klotzbach, the seven storms so far in 2015 have been unusually strong: Northwest Pacific Accumulated Cyclone Energy (ACE) was at record high through May 11 (78.1), just ahead of the old record of 77.7 in 1957. The early and violent start to 2015 typhoon season is due, in part, to exceptionally warm ocean temperatures in the typhoon breeding region between 5 - 10°N near the Date Line. These temperatures have been over 2°C (3.6°F) above average in recent months, due to a strengthening El Niño event.

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

Jeff Masters