Hurricane Hunters Find 50 mph Winds in 90L; Cat 3 Noul Aims at Philippines

An Air Force hurricane hunter aircraft measured winds in excess of tropical storm force on Thursday morning inside Invest 90L, the area of disturbed weather off the Southeast U.S. coast. However, the aircraft found no well-defined center, and 90L lacked enough heavy thunderstorm activity for NHC to name the system Subtropical Storm Ana as of 11 am EDT Thursday. The aircraft found a large area of 40 - 50 mph surface winds about 100 - 200 miles off the central and northeast coast of South Carolina. Winds of this strength were also measured by a 7:23 am EDT Thursday pass of the Rapidscat instrument on the International Space Station. (Note that in their In their 2 pm EDT Thursday Tropical Weather Outlook, NHC judged that rain contamination of the wind data meant these winds were more likely 40 - 45 mph.) As of noon EDT Thursday, rainfall amounts of about one inch were estimated by radar to have fallen along the South Carolina coast to the northeast of Charleston from 90L, but long-range radar out of Charleston showed little change in the intensity of organization of the rain bands of 90L. Satellite loops show that 90L has a large, ill-defined circulation, with a thick band of heavy thunderstorms extending to the northwest of the center over South Carolina, and almost no heavy thunderstorms near the center of circulation. This is a typical appearance for a subtropical cyclone, which characteristically have a large, cloud-free center of circulation, with heavy thunderstorm activity in a band removed at least 100 miles from the center. As explained in wunderground's subtropical storm tutorial, a subtropical cyclone has characteristics of both tropical and extratropical cyclones. The difference between a subtropical storm and a tropical storm is not that important as far as the winds they can generate, but tropical storms generate more rain, and tropical storms have the potential to rapidly intensify into hurricanes, while subtropical storms do not.

Wind shear over 90L had fallen to a moderate 20 knots late Thursday morning, and water vapor satellite loops showed a large area of dry air to the west over the Southeast United States. This dry air is retarding development, thanks to strong upper-level winds out of the west driving the dry air into the core of 90L. Ocean temperatures were near 25 - 26°C (77 - 79°F), which is just at the limit of where a tropical storm can form.


Figure 1. MODIS satellite image of 90L taken at approximately 11:30 am EDT May 7, 2015. Image credit: NASA Worldview.


Figure 2. Radar image of 90L taken at 12:02 pm EDT Thursday May 7, 2015, from the long-range radar out of Charleston.


Figure 3. The 7:23 am EDT (11:23 UTC) Thursday pass of the Rapidscat instrument on the International Space Station showed winds of up to 55 mph (50 knots, purple colors) off the coast of South Carolina from 90L. These winds may be weaker, perhaps 45 - 50 mph, due to contamination of the signal by heavy rains.

Forecast for 90L
The 8 am EDT run of the SHIPS model predicted that wind shear over 90L would fall to the light range, 5 -10 knots, on Friday, which should allow 90L to organize into a subtropical storm by Friday at the latest. Steering currents are weak over the waters off the Southeast U.S. coast, so expect a slow and erratic motion for 90L. The 00Z Thursday morning runs of our two top models for predicting tropical cyclones tracks, the European and GFS models, both showed the system making landfall on Sunday, in North Carolina or northeastern South Carolina. In their 2 pm EDT Thursday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 80%, respectively. 90L will be capable of bringing winds of 55 - 65 mph to the coast on Saturday and Sunday, along with heavy rains of 4 - 6 inches. Steve Gregory provides additional perspective on 90L in his latest blog post.


Figure 4. MODIS satellite image of Typhoon Noul taken near 05 UTC May 7, 2015. At the time, Noul was a Category 2 storm with 105 mph winds. Image credit: NASA Worldview.

Dangerous Typhoon Noul headed for the northern Philippines
Typhoon Noul has undergone a period of rapid intensification, and had reached major typhoon status with 115 mph winds as of 8 am EDT Thursday. WIth plenty of deep, water water before it and wind shear a moderate 10 - 15 knots, continued intensification into a Category 4 storm appears likely as the storm heads towards the northern Philippines. Satellite loops show that Noul is a medium-sized storm with a tiny pinhole eye with a modest area of heavy thunderstorms. The outer bands of Noul will begin affection the Philippines on Friday, with landfall of the center expected to occur in northern Luzon Island near 6 pm EDT Saturday (22 UTC). Noul will encounter a trough of low pressure as it approaches the Philippines, which is expected to induce a more northwesterly track. This may cause the storm's eye to miss the Philippines, as predicted by the 00Z Thursday run of the European model. The northeast part of Luzon is mountainous, which could increase the risk for very heavy rains as Noul moves onshore or nearby, although a grazing landfall would put most of Luzon on the weaker western side of the circulation. Noul will be referred to as Dodong in the Philippines’ naming system.

Another tropical system, Tropical Depression Seven, is organizing to the east over Micronesia. TD 7 is expected to pass near Micronesia's Pohnpei Island this weekend as a Category 1 typhoon, and the storm will likely pass within 300 miles of Guam next week. Satellite loops show that TD 7 is not yet well-organized, but it does have a large area of heavy thunderstorms. TD 7 may pose a long-range threat to the Philippines or Japan, but it is too early to know.

An exceptionally busy early portion of typhoon season
Noul's formation date of May 3 marks the second earliest appearance on record for the Northwest Pacific's sixth named storm of the year, according to statistics of the Japan Meteorological Agency's database from 1951 - 2015 maintained by Digital Typhoon. The average is 1.8 storms before May 8. The record is held by 1971, when the sixth named storm of the year (Babe) formed on May 3, six hours earlier than Noul's formation time. If TD 7 develops into a named storm before May 19, which appears highly likely, it will break the record set on May 19, 1971 for the earliest formation of the Northwest Pacific's seventh named storm of the year. The early start to 2015 typhoon season is due, in part, to exceptionally warm ocean temperatures in the typhoon breeding region between 5 - 10°N near the Date Line. These temperatures have been over 2°C (3.6°F) above average, due to a strengthening El Niño event. Water temperatures are also unusually warm for this time of year across parts of the Northeast Pacific. This region has yet to see its first named storm of 2015, but the continued evolution of El Niño and the already-warm SSTs indicate that a busy hurricane season is quite possible in this area as well.

Noul will be the second tropical cyclone to affect the Philippines so far in 2015. The first was Tropical Storm Maysak, which hit the Philippines exceptionally early in the season--during Easter weekend, April 4 - 5. Fortunately, Maysak was weakening rapidly as it made landfall, and no deaths or significant damage were reported (though four people were injured after huge waves generated by Maysak hit them while they were taking selfies along the shoreline of Dipaculao town in Aurora province on April 4.)

All-time May heat record for Europe falls--in the first week of May!
Extreme heat roasted Italy this week, where the city of Catenanuova hit 41.9°C (107.4°F) on Wednesday, May 6. According to weather records researcher Maximiliano Herrera, this is the hottest May temperature ever recorded in Europe. The previous record was 41.7°C (107.1°F), set on May 17, 2006 in Andujar, Spain. The new European May heat record comes just one day after the earliest 40°C temperature ever recorded in Europe--a 40.4°C (104.7°F) reading at San Priamo in southeastern Sardinia, according to Herrera's stats.

Jeff Masters