Taiwan, China Brace for Cat 5 Meranti; TS Ian Churns Through Open Atlantic

The newest Jeff Masters/Bob Henson blog post is available at https://www.wunderground.com/blog/. Yesterday's post: Mammoth Super Typhoon Meranti may spare Taiwan a direct hit as it continues barreling toward a potentially destructive landfall in China. Now moving just north of due west at about 15 mph, Meranti will be located near the southern tip of Taiwan by around 8:00 am Wednesday local time (8:00 pm Tuesday EDT). The latest forecast from the Joint Typhoon Warning Center (JWTC) takes the center of Meranti within 50 miles of southern Taiwan, close enough to generate torrential rains, possible landslides, and significant wind damage. Meranti is expected to slam into the southeast coast of China early Thursday local time (8:00 pm EDT Wednesday), perhaps near or just south of the city of Xiamen (population 3.5 million) in China’s Fujian province.


Figure 1. Visible satellite image of Meranti on Tuesday evening local time, September 13, 2016. Image credit: NOAA-NASA and RAMMB/CIRA, courtesy Jon Erdman, weather.com (@wxjerdman).


Figure 2. WU depiction of the JTWC track forecast for Meranti as of 12Z (8:00 am EDT) Tuesday, September 13, 2016.

Meranti among the deepest typhoons in world records
Meranti is a very large and extremely powerful typhoon. Its highest 1-minute sustained winds were 185 mph on Tuesday morning, according to the JWTC. This puts Meranti ahead of Cyclone Winston for the strongest sustained winds for any tropical cyclone of 2016 thus far. (Winston’s top winds were reduced from 185 to 180 mph in post-storm reanalysis.)

Meranti is even more impressive than Winston in another way. Because Meranti is so large, its central pressure is even lower than would be the case for a smaller storm that had the same peak winds. At 1250Z (8:50 am EDT) Tuesday, the Japan Meteorological Agency analyzed Meranti’s central pressure at 890 millibars. This puts Meranti in the elite pantheon of the deepest tropical cyclones ever recorded anywhere on Earth. Several others have had 890 mb central pressure, but only a few have dipped below that mark, including 2 hurricanes in the Atlantic, 1 hurricane in the Northeast Pacific, and 13 typhoons in the Northwest Pacific:

Typhoon Tip (1979) - 870 mb
Hurricane Patricia (2015) - 872 mb
Typhoon June (1975) - 875 mb
Typhoon Nora (1973) - 875 mb
Typhoon Ida (1958) - 877 mb
Typhoon Kit (1966) - 880 mb
Typhoon Rita (1978) - 880 mb
Typhoon Vanessa (1984) - 880 mb
Typhoon Nancy (1961) - 882 mb
Hurricane Wilma (2005) - 882 mb
Typhoon Forrest (1983) - 885 mb
Typhoon Irma (1971) - 885 mb
Typhoon Megi (2010) - 885 mb
Typhoon Nina (1953) - 885 mb
Typhoon Marge (1951) - 886 mb
Hurricane Gilbert (1988) - 888 mb

Most of these typhoon readings are direct measurements, collected aboard reconnaissance flights that were conducted for decades across the Northwest Pacific. With the advent of satellite imagery, regular reconnaissance missions into typhoons were dropped in 1987. It’s possible that several other post-1987 typhoons had central pressures below 890 mb that could not be accurately inferred via satellite. Some of the readings above have been rounded to the nearest 5 mb by the Japan Meteorological Agency, according to WU member 1900hurricane. He adds that Typhoon Judy (1979) had a reconnaissance-measured pressure of 887 mb that’s not part of the JMA database. Thanks to WU member SPShaw for compiling this list.

According to Phil Klotzbach (Colorado State University), only two Northwest Pacific typhoons aside from Meranti are known to have maintained 185-mph sustained winds for at least 18 hours: Tip (1979) and Haiyan (2013).


Figure 3. Visible (left) and infrared (right) VIIRS satellite imagery of the eye and eyewall of Super Typhoon Meranti as of 0508 (1:08 am EDT) Tuesday, September 13, 2016. Image credit: NOAA-NASA and RAMMB/CIRA, courtesy Dan Lindsey (Colorado State University), @DanLindsey77.


Figure 4. Radar image of Super Typhoon Meranti taken at 12:40 EDT September 13, 2016 (12:40 am local time on September 14.) Image credit: Taiwan Central Weather Bureau.

The outlook for Meranti
Even a glancing blow from Meranti is likely to produce significant damage in Taiwan. Meranti is so large that winds above tropical storm force and torrential rains can be expected over much of the island, with much higher winds near the center. The tall mountains of southeast Taiwan will wring out huge amounts of moisture as the storm approaches, with localized rainfall amounts of 25” or more quite possible along east-facing slopes. In addition, enormous waves will batter the southeast coast. Fortunately, this area is sparsely populated, and Meranti is moving at a good clip, which will reduce the chance of even higher rainfall amounts. Taiwan’s second-largest city, Kaohsiung, is located along the nation’s southwest coast, which could get hurricane-force winds as Meranti sweeps by to its south.

Storm surge will not be the biggest threat from Meranti in Taiwan, according to surge expert Hal Needham. “Tropical cyclones have trouble generating substantial storm surge in Taiwan because of the offshore water depth off the east coast is quite deep. Powerful typhoons approach from the east and would need either shallower offshore water or large inlets and bays to generate high storm surge. Those factors are missing from the east coast,” said Needham in an email. “The offshore water depth is more shallow along the west coast, which is also more populated. However, the strongest typhoon winds along a westward-facing coast are blowing offshore because of the counter-clockwise circulation. Typhoons will try to build up storm surge along the ‘back side’ of the storm, but this is not very efficient anywhere in Taiwan.”


Figure 5. Aqua/MODIS image of Marenti at 0510Z (1:10 am EDT) Tuesday, September 13, 2016. Image credit: NASA.

Potential impacts in China
Meranti’s worst impacts may well be in China. Especially if the typhoon avoids a direct hit on Taiwan, it will weaken only partially before reaching the China coast, so there is the potential for major wind damage and storm surge. Should Meranti strike just south of Xiamen, that city and its major port would be at risk of surge impacts. Given the mountainous terrain of China’s Fujian province, we can expect widespread torrential rainfall as a weakening Meranti slows down and grinds its way inland.

Meranti’s projected track is very similar to that of another super typhoon that struck Taiwan back in early July. Super Typhoon Nepartak maintained Category 5 strength with sustained winds of 160 mph and a central pressure of 900 mb until it was just 12 hours from landfall in Taiwan on July 7, 2016. Nepartak made landfall on the southeastern shore of Taiwan as a Category 4 super typhoon with top sustained winds of 150 mph, as estimated by the the Joint Typhoon Warning Center (JTWC), with a central pressure estimated at 930 mb by the Japanese Meteorological Agency (JMA). Nepartak struck the sparsely populated southeast coast of Taiwan and moved offshore north of Kaohsiung, limiting the damage from the storm. Three deaths in Taiwan were blamed on Nepartak, along with $33 million in agricultural damage. National Taiwan University (NTU) buoy NTU2 (located about 170 km southeast of Taitung, Taiwan) recorded a surface pressure of approximately 897 mb as the eye passed over near 8 am EDT July 7. If verified, this would have ranked as the lowest surface pressure ever measured by a buoy in world history. However, we received this update today by email from Ching-Ling Wei from the Institute of Oceanography, National Taiwan University: ”We have recovered the barometer at NTU2 during a buoy service cruise in early August and sent it to the Taiwan's Central Weather Bureau for calibrating the pressure sensor. After a carefully calibration procedure, we corrected the pressure data and obtained the lowest atmospheric pressure of 911.5 hPa instead of 897 hPa when the center of Nepartak was the closest to NTU2.” You can check out the National Taiwan University buoy website http://po.oc.ntu.edu.tw/ for  near-real time data as Super Typhoon Meranti passes by their two buoys. It appears, though, that the buoys lie too far to the north of Meranti’s track to receive hurricane-force winds.


Figure 6. Buoy NTU2 of the Institute of Oceanography, National Taiwan University recorded a lowest atmospheric pressure of 911.5 mb in Super Typhoon Nepartak when the storm made its closest pass on July 7, 2016. A camera on the buoy recorded these boating-unfriendly conditions during the typhoon.

The encounter with the high mountains of Taiwan destroyed the inner core of Nepartak, resulting in the surface circulation separating from the circulation at mid-levels of the atmosphere. A much weakened Tropical Storm Nepartak made landfall in mainland China day later, causing torrential rains that triggered flooding that killed 108 people and caused over $1.4 billion in damage. Meranti should experience less disruption from Taiwan’s mountains than Nepartak, given its more southerly track. According to the National Meteorological Center of China, the region of the coast where Meranti is expected to make landfall received over four inches of rain during the past ten days. It is likely that the soils are near saturation, and widespread destructive flooding can be anticipated from Meranti’s rains.

In the early afternoon Tuesday (U.S. EDT) Meranti was passing very close to two islands owned by the Philippines. At noon EDT Tuesday (midnight local time on Wednesday) , winds at Basco Radar, Philippines were sustained (10-minute average) at 90 mph and the pressure was 936 mb. At 1 am local time, winds at nearby Itbayat were sustained at 112 mph, with a pressure of 934 mb.

Storm chaser James Reynolds is on the southern tip of Taiwan, and will be posting updates to his Twitter feed.

Tropical Storm Ian churning the central Atlantic
Tropical Storm Ian was in the central Atlantic on Tuesday morning, about 900 miles east-southeast of Bermuda, headed north-northwest at 13 mph. Ian was in an environment not conducive for intensification, with wind shear a high 20 knots. Shear is expected to let up only a little this week, making it unlikely Ian will ever attain hurricane strength before getting absorbed by a cold front on Saturday. Ian is not a threat to any land areas.


Figure 7. Regional radar for Florida at 11 am EDT Tuesday, September 13, 2016, showed bands of showers from 93L impacting the coastal waters of Florida.

93L over central Florida showing development as it moves inland
An area of low pressure (Invest 93L) was located just west of Melbourne, Florida on Tuesday morning, and was headed inland, to the north-northwest, at about 10 mph. Satellite images and radar out of Melbourne, Florida showed that 93L was growing more organized Tuesday morning, with an increase in heavy thunderstorm activity, low level spiral bands beginning to form, and some rotation to the cloud pattern beginning to appear. The disturbance was battling high wind shear of 20 - 25 knots. The system will bring heavy rains to much of Florida and portions of southern Georgia on Tuesday. In their 2 pm EDT Tuesday Tropical Weather Outlook, NHC gave this system 2-day and 5-day development odds of 40%. This system looked a lot like a tropical depression on radar late Tuesday morning, and was generating sustained winds of 31 mph, gusting to 38 mph, at the Buoy 41009 (23 miles east of Cape Canaveral) at 11:50 am EDT.

95L off the coast of Africa may develop
A large tropical wave (Invest 95L) emerged from the coast of Africa Monday night, and was headed west-northwest at about 10 - 15 mph towards the Cabo Verde Islands. Satellite images late Tuesday morning showed that this wave was well-organized, with plenty of spin and heavy thunderstorm activity. With wind shear a moderate 10 - 20 knots, a moist atmosphere and warm SSTs near 27.5°C (81.5°F), 95L is likely to develop into a tropical depression late this week in the central tropical Atlantic, as predicted by the 0Z Tuesday runs of our three reliable models for predicting tropical cyclone genesis—the GFS, European, and UKMET models. The storm will mostly track to the west-northwest over the next five days, into a region of ocean where few storms eventually end up hitting the Lesser Antilles Islands. However, it is too early to assume that 95L will recurve to the north and northeast without ever affecting any land areas. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave this system 2-day and 5-day development odds of 30% and 50%, respectively.


Figure 8. Visible satellite image of Hurricane Orlene as of 1500Z (11:00 am EDT) Tuesday, September 13, 2016. Image credit: NOAA/NESDIS.

Hurricane Orlene on the decline
After topping out as a high-end Category 2 storm with top sustained winds of 110 mph, Hurricane Orlene is now on the downswing. Located about 600 miles west-southwest of Cabo San Lucas, Mexico, as of 11 am EDT Tuesday, Orlene was crawling north-northeast at just 5 mph, with top sustained winds down to 100 mph. A weakness in the upper-level ridge north of Orlene will keep steering currents very weak until Thursday, when the hurricane should resume a westward motion that will keep it away from the Mexican coast. Orlene is over marginally warm waters of 26-27°C, and its slow motion will allow cooler waters to be churned up, so the weakening trend should continue. Orlene is the 10th hurricane of the surprisingly busy East Pacific season of 2016.

Bob Henson and Jeff Masters