Emily Headed Out to Sea; Typhoon Noru Threatening Japan

Tropical Depression Emily was headed northeastwards at 14 mph away from the U.S. coast late Tuesday morning, after bringing heavy thunderstorms, torrential rain, and scattered wind and flood damage during its traverse of Central Florida Monday afternoon through early Tuesday morning. In its “best-track” archive, which has the most accurately determined locations of every tropical cyclone, the National Hurricane Center is now saying that Emily officially spun into life at 2 am EDT Monday just off the Gulf Coast of Florida, and made landfall with sustained winds of 45 mph near 10:45 am EDT, just south of Tampa. According to the University Corporation for Atmospheric Research's Michael Lowry, with only 8 hours from formation to landfall, Emily is one of the quickest hitting U.S. landfalls in past 34 years; only 4 of 121 were quicker.

Emily flooded many roads in the Tampa Bay area, and strong winds forced the closure of the Sunshine Skyway, a key Tampa bridge. A wind gust of 57 mph was reported in the Tampa Bay area, at the Skyway Fishing Pier 5 miles south-southeast of Fort DeSoto Park, at 10:53 am EDT Monday, near the time of Emily’s landfall. Emily knocked out power to 18,000 Florida customers, and minor roof damage was reported near Bradenton, East Naples, and Fort Myers Beach.

Figure 1. Tropical Storm Emily as seen by the MODIS instrument on NASA’s Terra satellite at 11:55 am EDT July 31, 2017. Emily made landfall just south of Tampa Bay, Florida, about 70 minutes before this image was taken. Image credit: NASA.

Forecast for Emily

The forecast for Emily is very straightforward, with the models agreeing on a path across the open Atlantic a few hundred miles offshore of the Southeast U.S. coast. Emily is a small storm, and its heavy rains will remain over the water. By Thursday, if not sooner, Emily should lose its tropical characteristics and be declared post-tropical. Emily will not trouble any more land areas with heavy rain or high winds.

Quiet elsewhere in the Atlantic

Other than Emily, the Atlantic is quiet, with NHC making no mention in their 8 am Tuesday Tropical Weather Outlook of any threat areas to be concerned with over the next five days. We do, however, need to watch a tropical wave predicted to come off the coast of Africa on Wednesday. The 0Z Tuesday run of the GFS model predicted development of this wave occurring early next week in the Central Atlantic, as the system moved west towards the Lesser Antilles Islands. The more recent 6Z Tuesday run of the GFS model did not support this idea, but the wave has considerable support for development among over 30% of the 70 ensemble members of the 0Z Tuesday runs of the GFS and European models.

The Weather Company’s Michael Ventrice is tracking the passage of a Convectively Coupled Kelvin Wave (CCKW), which will move through the tropical Atlantic this week. Passage of the CCKW is likely to leave more favorable conditions for tropical storm formation in its wake for next week. See our detailed explainer on CCKWs for more background.

Figure 2. NASA-NOAA's Suomi NPP satellite captured this infrared image of Super Typhoon Noru in the Northwest Pacific on Sunday, July 30, 2017 at 11:50 am EDT (1550 UTC). Two hours after this image was taken, Noru was rated a Category 5 storm with 160 mph winds. Image credit: University of Wisconsin-Madison/CIMSS/William Straka III

Typhoon Noru poses a growing threat to southern Japan

Residents of Japan’s southern islands need to keep a close eye on Typhoon Noru. Noru was a strong Category 2 storm as of 12Z Tuesday, with top sustained winds (1-minute) of 90 knots (105 mph) as estimated by the Joint Typhoon Warning Center (JTWC). After hurtling to Category 5 intensity on Sunday, the typhoon weakened gradually on Monday as it lost the benefit of a high-altitude outflow channel. However, Noru is expected to re-intensify as it moves slowly northwest toward Japan, where it will encounter slightly warmer waters (above 30°C or 86°F), and into a region with more favorable upper-level winds.

Noru’s northwest track is expected to bend slightly westward as it moves around a compact upper-level high parked near South Korea and the Sea of Japan. This is good news for Japan’s key population centers, including Tokyo, as it would take the typhoon well to their southwest. The large southern island of Kyushu, and the smaller archipelago of the Ryukyu Islands, may not be so lucky. By this weekend, the JTWC track brings Noru toward the west coast of Kyushu as a Category 3 storm. Such a track would put Kyushu on the more dangerous right-hand side of the typhoon. The official three-day outlook from the Japan Meteorological Agency angles Noru more toward the west over the next three days, which would bring the strongest impacts into the more sparsely populated Ryukyu Islands. A crucial question is how quickly the small upper high to the north of Noru breaks down, which is very difficult to predict at this point. The cone of uncertainty for Noru is, in reality, larger than is currently being depicted, given the higher-than-usual uncertainties in the evolution of the steering flow for the typhoon.

For what it’s worth, the operational runs of both the European and GFS models re-intensify Noru into a fearsome super typhoon. The 0Z Tuesday run of the Euro model took Noru on a track similar to the JTWC forecast, looping just to the west of Kyushu, while the 0Z and 6Z Tuesday runs of the GFS moved Noru on a slower, more northward track that would affect Kyushu as well as parts of central Japan. Both models deepened Noru below 900 mb by this weekend, which would imply the possibility of a Category 5 supertyphoon, but these values are very likely unrealistic. This may be a good example of the current tendency of global models to over-deepen strong tropical cyclones at subtropical latitudes (roughly north of 25°N). Until recent years, the global models featured resolution that was too coarse to replicate the lowest pressures at the heart of strong tropical cyclones. Today, the upgraded, higher-resolution models can produce very low surface pressures more readily, but they do not fully account for the ocean-atmosphere interaction across subtropical regions. At these latitudes, late-summer ocean temperatures can be very warm over a very shallow layer that is quickly disrupted by a strong hurricane or typhoon. (Thanks to Julian Heming, UK Met Office, for this background.) We should look at the HWRF model, which is our best intensity model, for guidance on how strong Noru might get. The 06Z Tuesday run of the HWRF model rebuilds Noru to Category 4 strength with 140 mph winds, and predicts a track that would take the storm well west of Kyushu.

Figure 3. WU tracking map for Typhoon Noru as of 8 am EDT (12Z) Tuesday, August 1, 2017, based on forecasts from the Joint Typhoon Warning Center.

Bob Henson co-wrote this post.