After an eerily quiet August, the tropics from Atlantic to Pacific are now looking a lot more like one would expect for early September. There’s a tropical storm and a hurricane in the Atlantic, a strong typhoon headed toward a high-impact encounter with South Korea, and a new depression in the East Pacific that’s likely to bring heavy rain to the Baja Peninsula and perhaps even some much-needed showers to parts of Southern California.
The most immediate threat to land comes from Typhoon Hinnamnor, a former category 5 super typhoon that weakened to category 1 strength, then reorganized and resurged on Saturday. As of 8 a.m. EDT Sunday, Hinnamnor was a category 3 equivalent with top sustained winds of 120 mph, according to the Joint Typhoon Warning Center. Hinnamnor was over the South China Sea about 300 miles southeast of Shanghai, moving north at roughly 10 mph.
The Yangshan Port near Shanghai, one of the world’s largest ports for container ships, was closed as Hinnamnor loomed offshore, complicating ship travel across the area, though no landfall in China is expected. Heavy rains lashed Taiwan, and strong winds caused more than 43,000 power outages there.
Tropical cyclone interceptor James Reynolds documented Hinnamnor’s passage near Miyakojima on Japan’s Miyako Island.
Hinnamnor was in a short-lived sweet spot for reintensification on Sunday. Pulling away from cooler upwelled waters as it accelerated northward, Hinnamnor was taking advantage of very warm sea surface temperatures (SSTs around 30 degrees Celsius or 86 degrees Fahrenheit, up to 2°C above average). A powerful upper low in far northeast China was pulling Hinnamnor poleward while providing a strong outflow jet at the storm’s top.
Hinnamnor could hit a second peak of category 4 strength late Sunday or early Monday local time, before wind shear begins to increase sharply, injecting dry air into the heart of the storm, and Hinnamnor begins to pass over cooler SSTs. These factors will be kicking in just as Hinnamnor is approaching the southeast tip of South Korea, so it’s unclear exactly how strong Hinnamnor’s top winds will be if and when it makes landfall. Update: At 8 a.m. EDT Monday, Hinnamnor was still packing category 3 winds of 100 knots (115 mph). Located about 230 miles southwest of Busan and moving north-northeast at 16 knots (19 mph), Hinnamnor will likely make landfall near or just west of Busan on Tuesday morning local time toward the upper end of category 2 strength.
Regardless of Hinnamnor’s core intensity at landfall, there’s more confidence that the typhoon will pack a large field of damaging wind as it approaches. Hinnamnor has expanded through its ups and downs and will continue to grow even larger as it moves poleward. Gale force winds span more than 400 miles, and hurricane force winds more than 200 miles.
As the typhoon’s moisture-packed winds encounter mountainous terrain, widespread rains of 3-10 inches can be expected across South Korea and parts of North Korea, with pockets of 10-20 inches or more bringing potential for flash floods and mudslides. Major power outages can also be expected. Hinnamnor’s trajectory may keep the largest storm surge potential offshore over the Korea Strait, but some areas of damaging surge are quite possible.
Only five typhoons of major-hurricane strength (Category 3 or stronger) are on record as passing within 100 nautical miles (115 miles) of Busan (see Figure 2 below). Typhoon Maemi (2003) – which made landfall with top sustained winds of 105 mph, according to JTWC – was the strongest cyclone to strike South Korea since Typhoon Sarah of 1959 (top sustained winds at landfall 115 mph) in records dating back to 1904. A recent analog for Hinnamnor is Typhoon Maysak, which followed a north-northeast track similar to Hinnamnor and clipped the South Korea coast near Busan as a category 2 storm.
Tropical Storm Earl may become major hurricane in open Atlantic
One of the more leisurely storm developments in recent Atlantic history continued at its gradual pace over the weekend. Tropical Storm Earl was born on Friday night, September 2, after its parent “invest”, 91L, moved slowly across the Main Development Region. Dry air inhibited Earl’s showers and thunderstorms (convection) during its MDR crossing, but the storm’s broad, well-established circulation sharpened on Friday, allowing it to bypass the tropical-depression stage.
As noted by Tomer Burg, Earl took 10 days from its first mention in an NHC Tropical Weather Outlook to become a named storm.
As of 11 a.m. EDT Sunday, Earl’s top sustained winds were 50 mph. The storm was only about 85 miles north-northeast of St. Thomas, U.S. Virgin Islands, but there were no watches or warnings for any land areas. The Greater Antilles are on Earl’s weaker left-hand side, and Earl’s gale-force winds extended only about 25 miles in that direction. Rainbands stretching across Puerto Rico and the Virgin Islands were more boon than bane for the drought-stricken region. Update: At 11 a.m. EDT Monday, Earl’s top winds had increased to 65 mph as the storm moved north-northwest at 5 mph.
Forecast for Earl
Earl maintained a distinct central core of strong convection just north of the Lesser Antilles on Sunday, but reconnaissance flights confirmed that Earl’s low-level center is near the west edge of the convection, a shear-induced displacement. Earl is passing over waters with moderately high oceanic heat content and very warm SSTs (around 29 degrees Celsius or 84 degrees Fahrenheit).
Earl will be contending with moderate wind shear of 10-15 knots through Monday, increasing to 20-25 knots from Monday into Tuesday. However, Earl will continue to pass over warm SSTs and will benefit from an increasingly moist atmosphere (mid-level relative humidity increasing from 50-55 percent to around 60 percent by Tuesday).
These mixed signals have led to some model disagreement on Earl’s pace of strengthening. The HWRF intensity model projects Earl will reach hurricane strength by Tuesday and perhaps category 2 strength by Wednesday, whereas the HMON is about a day later on hurricane strength.
The protracted saga of Earl may continue for some time. The official National Hurricane Center forecast at 11 a.m. Sunday called for Earl to reach major hurricane strength by Friday, as the storm recurves to the northeast across the unusually warm Atlantic subtropics. Fortunately, there is strong model agreement on a northward track for several days, and then recurvature southeast of Bermuda. Earl’s antics are thus not expected to cause any major land impacts, though Bermudans should keep an eye on Earl’s progress.
Danielle continues to impress in central North Atlantic
The year’s first Atlantic hurricane remained robust on Sunday at an unusually high latitude. At 11 a.m. EDT, Hurricane Danielle was about 1000 miles west of the Azores at latitude 38.1 north, packing top sustained winds of 80 mph. Danielle will continue on a harmless track this week, gradually accelerating east-northeast across the open Atlantic. Update: At 11 a.m. EDT Monday, Danielle’s top sustained winds were 85 mph after having peaked at 90 mph early Monday.
SSTs in early September are typically at or just below the 26-degree-Celsius threshold for tropical development at Danielle’s location, but a widespread marine heat wave has pushed SSTs close to 27 degrees Celsius. Light wind shear of around 5 knots has also given Danielle a boost, and wind shear should remain no more than about 15 knots through Wednesday. NHC is predicting Danielle to peak at sustained winds of 90 mph on Monday before embarking on a slow decline. Still, it may be Friday before Danielle becomes a strong post-tropical cyclone. Its remnants will reach Europe next week.
The next Cabo Verde wave, moving off the west coast of Africa on Sunday, likely will be the next system of concern in the Atlantic. NHC gives this disturbance a near-zero chance of development through Tuesday but a 20% chance by Friday. Update: In the Tropical Weather Update issued at 2 p.m. EDT Monday, NHC raised the 2- and 5-day odds of development to 20 and 50 percent, respectively.
Tropical Depression 12E a potentially dangerous storm for Baja
In the eastern Pacific a few hundred miles south of the southern coast of Mexico, Tropical Depression 12E formed at 11 a.m. EDT Sunday. Satellite images on Sunday afternoon showed that TD 12E was large and disorganized, and its large size will preclude rapid intensification in the short term. However, the system has favorable conditions for intensification, with moderate wind shear of 10-15 knots, warm SSTs near 29 degrees Celsius (84°F), and a moist atmosphere with a mid-level relative humidity near 85%. Update: TC 12E was upgraded to Tropical Storm Kay at 3 p.m. EDT Sunday. Kay’s top winds had intensified to 60 mph at 11 a.m. EDT Monday, and a tropical storm watch was in effect for the Baja California peninsula south of Loreto and Puerto San Andresito. Kay is now predicted to reach hurricane strength by Tuesday.
The top intensity models and the official NHC forecast are quite bullish on development of TD 12E, and the depression is likely to become a dangerous category 2 or stronger Hurricane Kay by Wednesday as it moves west-northwest to northwest, roughly parallel to the Pacific coast of Mexico. Along the way, the system is expected to produce 1 to 3 inches of rainfall, with isolated storm totals of 5 inches, across coastal portions of southwestern Mexico from Guerrero northwestward to Jalisco.
On Thursday, when TD 12E is expected to pass the southern tip of Mexico’s Baja Peninsula, the storm will encounter sharply lower sea surface temperatures associated with the cold, southward-flowing California Current. These cooler waters, in combination with potential land interaction with the rugged Baja Peninsula, should substantially weaken the system. TD 12E is expected to continue on a course roughly parallel to the Baja Peninsula, and moisture from the system could push into extreme southern California beginning on Saturday. Although rain would be welcome, any strong offshore winds or dry lightning from this system could enhance the wildfire threat across parts of the region, where a record heat wave has made the vegetation dangerously combustible.
Tropical cyclones are rare visitors to California. Since 1850, Southern California has experienced gale-force winds from seven tropical cyclones or their remnants. Most notable were a September 1939 tropical storm that hit near Long Beach and an 1858 hurricane that passed very near San Diego.
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