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Hurricane Dolores Hits Category 4 Strength

By: Bob Henson 7:37 PM GMT on July 15, 2015

A pulse of rapid intensification late Tuesday and early Wednesday pushed Hurricane Dolores to borderline Category 4 intensity in the Northeast Pacific. Dolores’s peak winds surged from 85 mph at 3:00 pm EDT Tuesday to 130 mph at 3:00 am Wednesday, which translates to a leap from Category 1 to Category 4 status in just 12 hours. The rapid intensification leveled off this morning, with Dolores’s peak winds at 9:00 am EDT Wednesday holding at 130 mph. Dolores is now heading west-northwest at 6 mph on a track somewhat south of earlier predictions, which will keep the hurricane over warmer water for a longer period. Dolores has a well-defined eye surrounded by strong thunderstorms, although the coldest cloud tops around the eye have warmed somewhat over the last few hours. Dolores is currently over 29°C (84°F) water, and vertical wind shear is quite low (5 – 10 knots). Some additional strengthening is thus possible later today into Thursday, although Dolores may not reach Category 5 strength unless another rapid intensification cycle gets under way; such cycles remain difficult to predict. By Friday morning, the center of Dolores should be moving over SSTs cooler than 26°C, with a gradual weakening expected thereafter.

Figure 1. An image of Hurricane Dolores collected by the GOES-East satellite at 1445 GMT (10:45 am EDT) on Wednesday, July 15. Image credit: NOAA Environmental Visualization Laboratory.

Figure 2. Infrared image of Hurricane Dolores from GOES-East, collected at 1800 GMT (2:00 pm EDT) on Wednesday, July 15. Image credit: NOAA Environmental Visualization Laboratory.

Earliest trio of Category 4s on record for Northeast Pacific
Of the season’s first four named storms in the Northeast Pacific, only Carlos has fallen short of Category 4 strength. Dolores is the earliest occurrence of the season’s third Cat 4 system in this basin, beating out Hurricane Frank, which became a Cat 4 on July 17, 1992. Northeast Pacific records go back to 1949. (Thanks to Brian McNoldy, University of Miami/RSMAS, for this factoid). It’s also the first time that three of the first four named systems in the Northeast Pacific have all reached Category 4 intensity. Dolores’s record comes no major surprise, given the persistently favorable wind shear and very high sea-surface temperatures induced by a strong and still-intensifying El Niño event. As noted by Michael Ventrice (WSI), a very strong pulse of the Madden-Julian Oscillation has influenced the eastern tropical Pacific for the last few weeks, enhancing the upward motion that fuels hurricane development. This MJO event is now subsiding, but the presence of a strong El Niño continues to favor above-average activity in the Northeast Pacific.

Especially noteworthy with this El Niño is the northward extent of the unusually warm water off Baja California and the U.S. Pacific states, meeting up with the “blob” of warm water off the Canadian west coast that’s persisted for months (Figure 3). Even with these impressive anomalies, SSTs are still far too cool to support tropical development immediately off the California coast. However, the zone of SSTs greater than 26°C, which is considered the threshold for maintaining a tropical cyclone, now extends several hundred miles further north than usual. This lays the groundwork for any hurricane recurving toward the southwest U.S. to maintain its strength longer than usual, all else being equal. Of course, the particulars of any given storm (its strength, structure, upper-level support, etc.) will determine how much of an impact might result. Over the next few weeks, residents of southern California, Arizona, and New Mexico will need to keep tabs on any hurricanes whose track would take remnants in their direction, as the risk for heavy rain, flash flooding, and even tropical-storm force winds could be elevated by the presence of such warm SSTs upstream.

Figure 3. Sea-surface temperatures (top) and anomalies (bottom) over the northeast Pacific Ocean, averaged for the week ending on Monday, July 13. Image credit: National Hurricane Center.

A weakening Typhoon Nangka approaches Japan
Dry air has taken its toll on Typhoon Nangka as it continues moving north-northwest at about 15 mph toward Japan. As of 1500 GMT (11:00 am EDT) on Wednesday, Nangka was located about 430 miles south-southwest of Iwakuni, Japan, with sustained winds now down to around 90 mph. Although wind shear remains low along Nangka’s immediate path (10 knots or less) and SSTs are above 26°C (79°F), the typhoon has been ingesting dry air from the west, eroding the convection on the left side of the eye over the last few hours. A strong ridge to the northeast of Nangka should keep the hurricane on a north-northwest bearing until landfall on Saturday local time near the islands of Shikoku and western Honshu. This track would put some of Japan’s biggest cities on the more dangerous eastern side of Nangka, so the weakening trend is good news indeed. The Joint Typhoon Warning Center projects Nangka to be a Category 1 storm at landfall. As noted by The Weather Channel’s Jon Erdman, heavy rains, high winds, and some power outages can be expected in the cities of Kyoto, Kobe, and Osaka, as Nangka comes ashore and encounters Japan’s mountainous islands. Further to the north, Tokyo may experience tropical-storm-level impacts. The north-northwestward path of the storm is nearly perpendicular to the coastline, which would maximize any coastal flooding from Nangka (a major storm surge is not expected, though).

Halola still on course for Japan
With top sustained winds of 85 mph, Typhoon Halola continues its steady trek west-northwest trek through the Northwest Pacific at about 17 mph. As of 11:00 am EDT Wednesday, Halola was located about 175 miles southeast of Wake Island. It now appears Halola will remain weak enough and far enough south of Wake Island to avoid major impacts there. Wind shear has kept Halola from strengthening as much as expected, but the shear should relax in a couple of days, which will give Halola a chance to intensify atop very warm SSTs. Halola could approach Japan next week, although the long-range GFS and ECMWF models suggest the typhoon will recurve before that point.

Elsewhere in the Pacific and Atlantic
The leisurely demise of Tropical Storm Enrique continues in the remote Northeast Pacific, about 1500 miles west of Cabo San Lucas, Mexico. Enrique’s top winds are 45 mph, and slow weakening is expected, with dissipation in the next couple of days.

There are no systems of interest in the Atlantic basin, and prospects are minimal for any tropical development there for at least the next several days.

Bob Henson


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.