Lackadaisical TS Karl May Strengthen; Paine in the Pacific; Malakas Hits Japan

The Northern Hemisphere tropics remain quite active during this final week of astronomical summer: we have a new hurricane in the East Pacific heading toward Mexico, plus a major typhoon in the Northwest Pacific plowing into western Japan. Meanwhile, hurricane watchers in the U.S. and Caribbean are casting their eyes toward Tropical Storm Karl, which has the potential to become a significant hurricane--though likely one that’ll remain a safe distance from land.

Now in its third day as a tropical storm, Karl is in no hurry to strengthen. Karl’s top sustained winds were estimated at a minimal 40 mph in the 11 am EDT advisory from the National Hurricane Center. Located in the central tropical Atlantic, about 900 miles east of the Leeward Islands, Karl continues to track almost due west at 13 mph. As was the case through the weekend, Karl’s low-level circulation was largely exposed on Monday morning, with most showers and thunderstorms (convection) swept to the northeast of the center. Vertical wind shear is fairly modest, at 10-15 knots, but that shear combined with a quite-dry middle atmosphere (relative humidity of 45-50%) has been enough to keep convection from gathering around Karl’s center.


Figure 1. Visible satellite image of Tropical Storm Karl as of 1515Z (11:15 am EDT) Monday, September 19, 2016. Image credit: NASA/MSFC Earth Science Office.

Outlook for Karl
Karl is likely to start flexing its muscles later this week. Sea surface temperatures along Karl’s path will be rising from around 28°C (82°F) on Monday to 29-30°C (84-86°F) by midweek, and the mid-level humidity will rise to around 60-65%, according to output from the 12Z Monday run of the SHIPS statistical model. Wind shear will drop to below 10 knots, giving Karl another big boost. The official NHC outlook brings Karl to hurricane strength by Friday. Models suggest that the bulk of this intensification may not occur until late in the week, despite the favorable conditions soon to evolve.

The upper-level pattern across North America and the North Atlantic will become more amplified late this week, with strong upper-level lows in the western U.S. and north-central Atlantic and ridges in the central U.S. and eastern Atlantic. Karl’s path should begin gradually angling west-northwest this week, enough to avoid the Caribbean, and models suggest that the North Atlantic low will extend far enough south late this week to pull Karl sharply northeastward by the time the storm gets to around 65°W to 70°W longitude. Less than 10% of the 50 European ensemble runs from 00Z Monday bring Karl far enough west to affect the U.S. All 20 GFS ensemble members from 00Z Monday keep Karl well to the east of the States, as does the 00Z Monday run of the UKMET model. These track results have been quite consistent over the last couple of days, which lends added support to the idea that Karl is unlikely to pose a U.S. threat.

Karl could easily affect Bermuda, depending on how sharply it recurves. If this year’s tendency holds, Karl could achieve its maximum strength at a fairly high latitude, around 30-35°N, another reason for Bermuda to pay close attention to Karl.


Figure 2. Tracks from the 20 members of the GFS model ensemble run (GEFS) from 06Z Monday, September 19, 2016, updated with data from 12Z Monday. Ensemble runs are produced by introducing small variations in the starting-point conditions to mimic uncertainty about the state of the atmosphere.

Adios, Julia
After five days, the National Hurricane Center has pulled the plug on irritating Tropical Storm Julia. NHC discontinued advisories on Julia on Sunday night, classifying the storm as a remnant low. Julia’s biggest impact may be posthumous: some of its moisture is now being pulled into a weak upper-level low and associated front over the Mid-Atlantic coast. Rainfall amounts of 2” - 4” will be widespread from eastern North Carolina to southeast Massachusetts, with higher localized amounts, especially toward the NC Outer Banks.


Figure 3. Enhanced infrared image of Invest 96L as of 1445Z (10:45 am EDT) Monday, September 19, 2016. Image credit: NOAA/NESDIS.

Strong tropical wave may develop in eastern Atlantic
The next solid chance at a named storm in the Atlantic is Invest 96L, located a couple hundred miles southwest of the Cabo Verde Islands. This wave has much more convection than Karl, and data from the ASCAT scatterometer suggests that a weak closed circulation has already formed. 96L’s thunderstorms are being nourished by a moist middle atmosphere (relative humidity around 65%). Wind shear will be fairly light (5 - 15 knots) for the next couple of days, and SSTs of 28-29°C are more than adequate for development. In its 8 am EDT Monday tropical weather outlook, NHC gives 96L a 70% chance of becoming a tropical depression by Wednesday and an 80% chance by Saturday. It’s quite possible that 96L will be Tropical Storm Lisa by midweek, if not sooner, but hurricane status may not be in the cards. The SHIPS model shows wind shear ramping into the 25 - 35 mph range by late this week as 96L heads northwest over progressively cooler waters. GFS and Euro ensembles indicate that the most likely outcome is for 96L to peak at tropical storm strength. We can expect 96L to remain far from any threat to land.


Figure 4. Infrared image from Japan’s Himiwari-8 satellite of Typhoon Malakas as of 1520Z (11:20 am EDT) Monday, September 19, 2016. Image credit: NOAA/CIRA/RAMMB/Colorado State University.

Major Typhoon Malakas heads into Japan
Significant impacts are likely as Typhoon Malakas grinds its way northeastward along the south coast of Japan’s main islands. Malakas passed through Japan’s far-flung Yaeyama Islands as a Category 4 typhoon over the weekend: the eye passed directly over the westernmost island, Yonaguni, where the Yonagunijima airport clocked wind gusts up to 100 mph. As of 12Z (8:00 am EDT) Monday, the Joint Typhoon Warning Center rated Malakas as a minimal Category 3 storm, with top sustained (1-minute) winds of 115 mph. Malakas was slamming into the island of Kyushu early Tuesday local time. At 12:05 am JST Tuesday (11:05 am EDT Monday), Kanoya Air Field reported a wind gust to 106 mph, with surface air pressure down to 973 millibars.

Malakas will weaken dramatically as it continues northeast along the coast. By the time it passes near Tokyo early Wednesday, Malakas should be down to weak tropical storm strength. However, torrential rains of 5” - 10” and resultant landslides will be a major concern across large sections of southern Japan, including much of Honshu. According to weather.com, the city of Takanabe reported 4.33” of rain in just one hour on Monday night local time.


Figure 5. Radar image of Typhoon Malakas, centered on the south end of Japan’s Kyushu island as of 0115 JST Tuesday, September 20, 2016 (12:15 pm EDT Monday). Rainfall rates at lower right are shown in millimeters per hour: 80 mm = 3.15”. Image credit: Japan Meteorological Administration.


Figure 6. Visible satellite image of Hurricane Paine as of 1559Z (11:59 am EDT) Monday, September 19, 2016.

Tropical Storm Watch for Baja California as Hurricane Paine spins up
The 11th hurricane of the year in the East Pacific is a Paine--literally. Now located about 350 miles west of Cabo San Lucas, Mexico, Hurricane Paine has intensified rapidly, with top sustained winds rocketing from just 40 mph at 11 AM EDT Sunday to 85 mph as of the 11 am EDT Monday advisory from NHC. Paine is likely at its peak strength, as the hurricane will soon be moving northwest over cooler waters and encountering greater wind shear. By the time Paine heads into the northern coast of Baja California on Wednesday, it should be little more than a weak tropical storm or depression. Since Paine’s recurving path could bring tropical storm-force winds east of its center onto land, the Mexican government has issued a Tropical Storm Watch from Punta Eugenia to Cabo San Quintin.

Some moisture from Paine (and a nearby upper low) will filter into the Southwest U.S. by midweek, although not as much as was delivered by Tropical Storm Newton several weeks ago. A few showers have already filtered into far Southern California, where any rainfall is welcome in the midst of a five-year-long drought.

For the years 1971-2009, the average number of hurricanes per year in the East Pacific was 8. Given that we’re now on #11 for 2016, this is a busy East Pacific season indeed! The record number of hurricanes in a single East Pacific season is 16, set in 1990, 1992, and 2014.

Bob Henson


Figure 8. Projected track for Hurricane Paine from the National Hurricane Center as of 15Z (11:00 am EDT) Monday, September 19, 2016.