WunderBlog Archive » Category 6™

Category 6 has moved! See the latest from Dr. Jeff Masters and Bob Henson here.

Subtropical Depression 7 Headed Towards Bermuda, but 90L is the One to Watch

By: Dr. Jeff Masters, 3:38 PM GMT on October 10, 2014

Subtropical Depression Seven formed in the Atlantic at 11 am EDT Friday. The depression, located about 590 miles south of Bermuda, was headed northwest at 10 mph, and Bermuda is the only land area the storm poses a threat to. A tropical storm watch has been posted for the island, and the 11 am EDT Wind Probability Forecast from NHC gave Bermuda a 14% chance of seeing tropical storm-force winds of 39+ mph, with the strongest winds expected to affect the island Saturday evening into Sunday morning. Satellite loops showed STD 7 had very little heavy thunderstorm activity near its center, with most of the action in a curved band well to the north of the center. This is characteristic of a storm that is not fully tropical, thus the designation of the storm as a subtropical depression. Sea Surface Temperatures (SSTs) were warm, near 29°C (84°F), and wind shear was moderate, 5 - 15 knots. These conditions are favorable for slow development, and the depression is likely to get the name Fay Friday evening or Saturday morning. Disturbances getting their start from a cold-cored upper level low like STD 7 have plenty of cold, dry air aloft, which retards development into a tropical system. I expect STD 7 will be named Subtropical Storm Fay instead of Tropical Storm Fay, if it intensifies at expected. STD 7 will recurve to the northeast out to sea on Sunday without troubling any other land areas. An Air Force hurricane hunter aircraft has been tasked to investigate STD 7 on Friday afternoon.

Figure 1. Latest satellite image of Subtropical Depression Seven.

Pay attention to Invest 90L east of the Lesser Antilles
An area of disturbed weather associated with a tropical wave located about 700 hundred miles east of the northern Lesser Antilles Islands on Friday morning has been designated Invest 90L by the National Hurricane Center. This disturbance has the potential to be trouble, and needs to be watched carefully. Invest 90L was headed west to west-northwest at about 10 mph. Satellite loops showed 90L had a modest amount of spin and heavy thunderstorm activity, and these thunderstorms were poorly organized. Water vapor satellite loops show a good degree of dry air surrounding 90L, and this will retard development. Sea Surface Temperatures (SSTs) were warm, near 28.5°C (83°F), and wind shear was light, 5 - 10 knots. These conditions are favorable for development. The 8 am Friday run of the SHIPS model predicted that conditions would remain favorable for slow development through Monday, with light to moderate wind shear and SSTs near 29°C (84°F), though the atmosphere is expected to dry as the disturbance moves to the north of Puerto RIco early next week. All three of our reliable computer models for predicting tropical storm formation, the European, GFS, and UKMET models, showed 90L developing by the middle of next week in their 00Z Friday runs. When multiple models predict development, the odds of formation are increased. In their 8 am EDT Friday Tropical Weather Outlook, NHC gave 90L 2-day and 5-day development odds of 10% and 20%, respectively. Given the high model support for 90L's development, I put the 5-day odds of development higher, at 40%. 90L's west-northwest trajectory will carry it to a point about 100 - 200 miles north of Puerto Rico on Monday, and near the Southeast Bahamas and Turks and Caicos Islands on Wednesday.

Figure 2. Latest satellite image of Invest 90L near the Lesser Antilles.

Typhoon Vongfong giving Okinawa an epic battering
Japan's Okinawa Island is receiving an epic battering from Typhoon Vongfong as the powerful storm steams slowly northward at 9 mph. Cooler waters, higher wind shear, and an eyewall replacement cycle had weakened Vongfong to Category 4 strength with 135 mph winds as of 8 am EDT Friday, according to the Joint Typhoon Warning Center (JTWC), and the Japan Meteorological Agency (JMA) showed Vonfong's central pressure had risen to 925 mb at 9 am EDT Friday, up from a low of 900 mb on Wednesday. Satellite loops show that Vongfong is still an impressive storm with a very large area of heavy thunderstorms and a prominent 17-mile diameter eye.

Figure 3. High resolution imagery from the VIIRS instrument on the Suomi NPP satellite shows a highly detailed view of the eye of Super Typhoon Vongfong on October 9, 2014 at 03:55 UTC. At the time, Vongfong was a Category 4 storm with 155 mph winds. Image credit: NOAA Environmental Visualization Laboratory.

Okinawa at risk of a direct hit from Vongfong
Tropical storm-force winds of 39+ mph of greater have buffeted Okinawa since 5:39 am EDT Friday (6:39 pm local time), and this large and slow-moving typhoon will keep tropical storm-force winds blowing on the island for an extraordinary long period of time--over 48 straight hours, until approximately 10 am EDT (11 pm local time) Sunday. Wind gusts as high as 81 mph have already been measured on Okinawa, along with sustained winds as high as 59 mph. Our two top models for predicting tropical cyclone tracks, the GFS and European, both predicted with their 06Z and 00Z Friday runs, respectively, that the eye of Vongfong would pass over Okinawa near 15 UTC (11 am EDT) Saturday. With the typhoon moving over waters that will gradually cool, and with wind shear expected to rise from the moderate range (15 - 20 knots) to the high range (>20 knots), Vongfong should weaken and be a Category 2 or low-end Category 3 typhoon at that time. JMA is forecasting 500 - 700 mm (20 - 28 inches) of rain for Okinawa and nearby islands, and forecasts top sustained winds of 100 mph with gusts to 145 mph for the Okinawa region. Wave heights are forecast at 13 m (over 40 ft) for Okinawa and the Amami Islands to the north.

Rapid weakening should ensue as Vongfong approaches the main Japanese island of Kyushu this weekend, with Category 1 strength likely at landfall. In their 00Z Friday runs, the European and GFS models predicted landfall would occur on Kyushu between 8 pm - 11 pm U.S. EDT time Sunday evening (00 - 03 UTC Monday.) Heavy rains from Typhoon Vongfong are expected to fall on soils already saturated by Typhoon Phanfone's rains last week, which could lead to much more severe flooding than was observed for Phanfone. Vongfong will also be moving slower than Phanfone was, potentially leading to higher rainfall amounts.

Storm Chaser James Reynolds is on Okinawa, and is posting updates and images to his Twitter feed.
Latest Japanese radar shows heavy rain bands of Vongfong affecting Okinawa.

Figure 4. Tropical Cyclone Hudhud as seen by Astonaut Reid Wiseman from the International Space Station at 9:30 am EDT October 10, 2014. At the time, Hudhud was an intensifying Category 1 storm with 85 mph winds. Image credit: Reid Wiseman.

Dangerous Tropical Cyclone Hudhud a threat to India
Category 1 Tropical Cyclone Hudhud in the Bay of Bengal is steadily intensifying as it heads west-northwest towards India, with sustained winds estimated at 85 mph at 8 am EDT Friday. The storm is under moderately high wind shear of 20 knots, and is over warm waters of 30°C (86°F)--conditions which favor continued modest intensification. Satellite loops show a well-organized system with plenty of low-level spiral bands and an increasing amount of heavy thunderstorm activity. On Friday morning (U.S. EDT time), the India Meteorological Department (IMD) was forecasting that Hudhud would have sustained winds of 130 - 140 kph (81 - 87 mph) at landfall, making it a strong Category 1 storm. JTWC was forecasting a stronger storm--Category 3 with 115 mph winds. IMD predicted a storm surge of 1 - 2 meters (3.3 - 6.6 feet) would occur near and to the right of where the center makes landfall. With warmer sea surface temperatures ahead of the storm and wind shear expected to be in the 15 - 20 knot range, intensification into at least a Category 2 cyclone appears likely before Hudhud hits the coast of northern Andhra Pradesh and southern Odisha between Visakhapatnam and Gopalpur on Sunday, October 12, near 06 UTC. Odisha was struck in 2013 by Category 4 Tropical Cyclone Phailin, which killed 45 people and did $700 million in damage. This death toll was extremely low, considering this is a region where 10,000 people died in a similar-strength cyclone in 1999. IMD provided excellent early warning information for Phailin.

Latest Hudhud warnings for India from the India Meteorological Department (IMD)
Latest Hudhud advisory from the India Meteorological Department (IMD).
India radar from Machilipatnam.

Hurricane expert Steve Gregory has his take on the tropics in a Friday afternoon post.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.