97L Close to Tropical Depression Status; Category 4 Megi Hammers Taiwian

A tropical wave located about 400 miles east-southeast of Barbados in the Lesser Antilles Islands late on Tuesday morning (Invest 97L) was headed west to west-northwest at 15 - 20 mph, and appears likely to develop into a tropical depression or tropical storm later on Tuesday. Satellite loops late Tuesday morning showed 97L did not yet have a well-defined surface circulation, though it appeared close to establishing one. The amount of heavy thunderstorm activity was modest at best, but upper-level outflow was very well established to 97L’s north. Aiding development was moderate wind shear of 10 - 20 knots and warm ocean waters of 29.5°C (85°F). Significant negatives for development included the storm’s forward speed of 15 - 20 mph, which was too fast for the storm to get itself properly aligned in the vertical, plus dry air. The 8 am EDT Tuesday SHIPS model output analyzed 55% relative humidity at mid-levels of the atmosphere over 97L, which is lower than optimal for tropical cyclone formation. The 12Z (8 am EDT) Tuesday balloon sounding from Trinidad, 500 miles to the west of 97L, showed several bands of dry air with humidities below 40% located between 618 mb and 300 mb in altitude. Water vapor satellite loops showed 97L was butting into a region of dry air that lay just east of the Lesser Antilles Islands. Lack of spin from being too close to the equator was less of a problem for 97L than before, as the system had worked its way northwards to a latitude of 12°N. This is far enough from the equator for the storm to be able to leverage the Earth’s spin and acquire more spin of its own. The outermost spiral rainband of 97L was bringing rain showers to Barbados late Tuesday morning, as seen on Barbados radar.


Figure 1. Latest satellite image of 97L.

Forecast for 97L
Model support for development of 97L over the next day or so remains high. Our top three models for predicting hurricane genesis—the GFS, UKMET and European models—all predicted in their 00Z Tuesday runs that 97L would develop into a tropical depression or tropical storm between Tuesday and Wednesday. In their 8 am EDT Monday Tropical Weather Outlook, NHC gave 97L 2-day and 5-day development odds of 90%. The Hurricane Hunters are in the air, and will investigate the storm on Tuesday afternoon. The next name on the Atlantic list of storm names is Matthew.

Invest 97L will continue west to west-northwest at 15 - 20 mph through Thursday, then slow down to a forward speed of 5 - 10 mph for the remainder of the week. The outer spiral bands of 97L will begin spreading over the Lesser Antilles Tuesday night, bringing high winds and heavy rains. The core of the storm will pass through the islands on Wednesday afternoon. It is unlikely that 97L will have time to intensify into a hurricane by then, though a strong tropical storm with 55 - 65 mph winds is quite possible. The strongest winds and heaviest rains of 4 - 8” can be expected over the islands just north of where the center of 97L is, including the islands of St. Lucia, Martinique, Dominica, and Guadaloupe. The storm will continue westwards on Thursday, and make its closest approach to the ABC islands of the Netherlands Antilles--Aruba, Bonaire, and Curacao--on Thursday night and Friday morning. These islands will be on the weak (left) side of the storm, and may escape receiving tropical storm winds. However, heavy rains of 2 - 4” can be expected, as predicted by the 06Z (2 am EDT) Tuesday run of the HWRF model.

As 97L passes through the southeastern Caribbean, it will be in an environment somewhat unfavorable for development. The southeast Caribbean is a well-known tropical cyclone graveyard, where scores of healthy-looking storms have died or suffered severe degradation. This is often due to the fact that the southeastern Caribbean is a place where the surface trade winds tend to accelerate, due to the geography and meteorology of the area. A region of accelerating flow at the surface means that air must come from above to replace the air that is being sucked away at the surface. Sinking air from above warms and dries as it descends, creating high pressure and conditions unfavorable for tropical cyclones. In addition, tropical cyclones passing near the coast of South America often suck in dry continental air from the land areas to the south. The last hurricane to pass through the southeastern Caribbean, Hurricane Tomas of 2010, degraded from a Category 1 hurricane to a tropical depression due to high wind shear and dry air as it moved across the region. Recent runs of the SHIPS model are showing moderate wind shear of 10 - 15 knots and some dry air for Thursday and Friday along 97L’s path, and these conditions may interfere with development. In addition, the Tuesday morning 00Z runs of the European and UKMET models predicted that 97L would move slightly south of due west and pass very close to the coast of South America on Friday, which would also inhibit development.





Figure 2. Forecasts from the 00Z Tuesday European (ECMWF) model ensemble (top) and GFS model ensemble (bottom) had a number of their 70 members predicting a hurricane for late in the week in the Caribbean (light blue dots.) The operational versions of the models, run at higher resolution (red lines), also showed the storm becoming a hurricane by ten days into the future. The European model showed a more westerly track for 97L, with a long-range threat to the Gulf of Mexico, while the GFS model predicted more of a threat to the U.S. East Coast.

Long range forecast for 97L
A large upper-level low pressure system is expected to separate from the jet stream and settle over the Mid-Atlantic states late this week, and the steering currents associated with this low are expected to be strong enough to pull 97L sharply to the north by the weekend, according to a majority of the Tuesday morning runs of the models. While the sharp right-hand turn in Figure 2 might look implausible, there are a number of cases of storms taking such a northward bend, especially in October, with the classic example being Hurricane Hazel (1954). This sharp turn is expected to occur on Friday night or on Saturday, and the exact timing of the turn has huge implications for who experiences the peak wrath of the storm. An earlier turn is being predicted by the GFS model, which would put the Dominican Republic and Haiti in the cross hairs for a direct hit early next week, with a long-range threat to the Bahamas and the U.S. East Coast later in the week. The European model and UKMET model forecast a later turn, resulting in Jamaica and Cuba being more at risk of a direct strike early next week, and Florida and the U.S. Gulf Coast being at risk later in the week. As one can see from the latest set of ensemble model runs (Figure 2), the uncertainties are high. 97L is expected to have favorable conditions for intensification this weekend as it heads north towards the islands, with low wind shear, very warm ocean waters, and a very moist atmosphere. The models are quite bullish on this storm being a hurricane when it makes its landfall early next week in the islands.

Ulika forms in the Central Pacific
In the Central Pacific, Tropical Storm Ulika formed on Tuesday morning. Ulika is not expected to threaten any land areas, and is forecast to pass several hundred miles to the southeast of Hawaii early next week as a tropical depression.


Figure 3. Churning waters in the Jhihtan Dam in Xindian district, New Taipei City, as Typhoon Megi hit eastern Taiwan on September 27, 2016. Taiwan went into shutdown on September 27 as the island faced its third typhoon in two weeks, with thousands evacuated, schools and offices closed across the island and hundreds of flights disrupted. Image credit: Sam Yeh/AFP/Getty Images.

Deadly Typhoon Megi slams into Taiwan
Bolting to Category 4 status just before landfall, Typhoon Magi crashed into central Taiwan at full force on Tuesday evening local time. CNN reported least four deaths and more than 300 injuries by late Tuesday, with close to 2.7 million homes without power. Megi’s top winds were assessed at 115 knots (132 mph) by the Joint Typhoon Warning Center at 06Z Tuesday (2:00 am EDT and 2:00 pm local time). Meg plowed ashore near Hualien City, where Josh Morgerman (@iCyclone) reported calm winds in the large eye of the typhoon at 1:55 pm local time. See the photo embedded at bottom for a spectacular view of waves smashing into the seawall at Hualien City.

Megi completed an eyewall replacement cycle just before reaching Taiwan, which allowed for a burst of intensification even as it approached the island. At 12Z Tuesday, the JTWC placed Megi’s center in the Taiwan Strait, midway between Taiwan’s west coast and the southeast coast of China (about 50 miles from each). Top sustained winds at 12Z were down to 100 knots (115 mph), making Megi a fast-weakening Category 3. Not surprisingly, Megi’s quick journey across the rugged mountains of Taiwan took a major toll on the integrity of its structure, but Megi will still pack some punch as it sweeps into China as a strong tropical storm or minimal typhoon. Mega is the third major typhoon to affect Taiwan in the last two weeks, following Super Typhoon Meranti (which passed just southwest of the island) and Typhoon Malakas (which passed just to the northeast). Meg’s landfall in southeast China will be close to the area where Meranti claimed at least 29 lives and caused at least $2.6 billion in damage.


Figure 4. Aqua/MODIS satellite image of Typhoon Megi at 0525Z (1:25 am EDT and 1:25 pm local time) Tuesday, September 27, 2016, just as Megi was making landfall in east-central Taiwan. Image credit: NASA.


Figure 5. Rainfall across Taiwan for the calendar day Tuesday, September 27, 2016, up through 10:30 pm local time (10:30 am EDT Tuesday). The scale at right is in millimeters; 100 mm = 3.94 inches. Image credit: Central Weather Bureau, Taiwan.

It was still too soon on Tuesday morning EDT to assess the full impact of Megi’s assault on Taiwan. Wind gusts above 90 mph were widespread, as reported by weather.com. Sustained winds reached 71 mph with gusts to 99 mph at 2:30 pm local time at Taipei’s Taiyuan International Airport, with a gust to 124 mph recorded at Wuqi on Taiwan’s west coast, according to Taiwan’s Central Weather Bureau. Wind damage may be widespread over northeast Taiwan in Yilan County, home to about half a million people. Meg’s path put coastal Yilan County just north of Megi’s large eyewall, and the typhoon’s fierce winds pushed upslope to produce torrential rains in the county’s mountainous western section. A total of 945 mm (37.20”) fell at Taipingshan in western Yilan County from midnight through 10:30 pm local time Tuesday, according to Taiwan’s Central Weather Bureau. By late Tuesday, the heaviest rains were wrapping into southwest Taiwan on the south side of Megi’s circulation, where 10” amounts were widespread.


Figure 6. Rainfall amounts topping 10” are possible along and near the coast of southeast China and in far South Korea over the next several days as Megi and its remnants move into China and eventually recurve toward the northeast. Shown above is cumulative precipitation for the six-day period starting at 06Z (2:00 am) Tuesday, September 27, 2016, from the GFS model. The scale at right is in millimeters; 100 mm = 3.94 inches. Image credit: tropicaltidbits.com

We will be back this afternoon with an update on 97L and the Pacific storms.

Jeff Masters and Bob Henson

Hualien port sea wall taking a beating earlier today as #typhoon #Megi hit #Taiwan pic.twitter.com/ckH38WgdPh

— James Reynolds (@EarthUncutTV) September 27, 2016

Figure 7. James Reynolds says: “Hualien port sea wall taking a beating earlier today as #typhoon #Megi hit #Taiwan.” See the associated video. Image credit: James Reynolds, @EarthUncutTV.