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Tropical Storm Niala Approaching Hawaii; Heavy Rains for Gulf Coast Likely From 99L

By: Jeff Masters 3:22 PM GMT on September 26, 2015

A Tropical Storm Watch and a Flash Flood Watch are posted for Hawaii's Big Island, as Tropical Storm Niala moves northwest at 8 mph on a course that will take it about 100 miles south of the Big Island on Sunday evening. With tropical storm-force winds expected to extend out up to 80 miles from the center at that time, the Central Pacific Hurricane Center in their 11 am EDT Saturday Wind Probability Forecast gave a 26% chance for South Point on the Big Island to receive tropical storm-force winds of 39+ mph. The bigger threat from the storm will be heavy rain, which could bring 6 - 12" of rain and dangerous flash floods to the Big Island on Saturday and Sunday.

Figure 1. Latest image from the South Hawaii radar.

Figure 2. Latest satellite image of Niala.

Niala is the record 7th named storm to form in 2015 in the North Central Pacific (between 140°W and the Date Line.) According to wunderblogger Dr. Phil Klotzbach, prior to 2015, the previous record for named storms in the North Central Pacific for an entire season was four, set in 1982. The other named storms that formed in the North Central Pacific in 2015 were Malia, Halola, Ela, Iune, Kilo and Loke. This year's record activity has been due to unusually low wind shear and record-warm ocean temperatures caused by the strong El Niño event underway.

99L in Gulf of Mexico to bring heavy rain to the Gulf Coast
A trough of low pressure is moving northwestwards across Mexico's Yucatan Peninsula, and is producing a large area of disorganized showers and thunderstorms over the northwestern Caribbean Sea and portions of Central America, as seen on satellite loops. On Saturday morning, NHC designated this area of interest Invest 99L. By Sunday, this activity will push into the Gulf of Mexico, where development into a tropical or subtropical depression could occur. However, an upper-level trough of low pressure over the Western Gulf of Mexico will bring high wind shear to the Gulf, limiting the potential for 99L to strengthen, and our top three models for predicting tropical cyclone genesis are showing little development of this system. The system will get pulled northwards to affect the U.S. coast from Louisiana to the Florida Panhandle Sunday afternoon through Tuesday, bringing heavy rains of 2 - 4". In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10% and 20%, respectively.

98L between Bermuda and the Bahamas of little concern
A non-tropical trough of low pressure (Invest 98L) is producing disorganized showers and a few thunderstorms over the western Atlantic Ocean several hundred miles south-southwest of Bermuda as the system drifts north to north-northwest at about 5 mph. With record warm ocean temperatures near 30°C (86°F) and wind shear in the moderate range, 10 - 20 knots, this disturbance may show some slow development on Saturday and Sunday. However, wind shear is predicted to rise to the high range, 20 - 30 knots, beginning on Sunday night. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 10% and 10%, respectively.

Little change to Ida
There is not much new to say about Tropical Depression Ida, which is wandering slowly over the Central Atlantic, well away from any land areas. Satellite images on Saturday morning showed Ida's center of circulation was fully exposed to view by high wind shear, and all of Ida's heavy thunderstorms were limited to the east side of the center. Ida will continue to move slowly in a region of weak steering currents for the next five days, and it is possible that high wind shear will destroy the storm by Tuesday, as suggested by Saturday morning runs of the GFS model.

Figure 3. MODIS image of Typhoon Dujuan as seen from NASA's Terra satellite on Saturday, September 26. Image credit: NASA.

Typhoon Dujuan bears down on Japan's Ryukyu Islands
Typhoon Dujuan, a Category 2 storm with 110 mph winds located about 325 miles south-southeast of Okinawa in Japan's Ryukyu Islands at 8 am EDT Saturday, is steadily intensifying as it heads northwest at 10 mph towards Taiwan. Wind shear is in the moderate range, 10 - 15 knots, and ocean temperatures are a very warm 29°C (84°F), conditions which favor intensification. Satellite loops on Saturday morning showed a large, well-organized storm with a huge 44-mile wide eye. Dujuan has taken on an annular appearance, with a large eye, thick eyewall, and very few low-level spiral bands. These type of storms are more resistant to weakening than ordinary, making Dujuan likely to maintain major typhoon status as it approaches Taiwan. The Joint Typhoon Warning Center (JTWC) projects that Dujuan will intensify to Category 4 strength by Sunday, and the storm is expected to pass near Taketomi-cho and Yonaguni-cho in Japan's Ryukyu Islands near 03 UTC Monday. The models have come into better agreement on the eventual fate of Dujuan, with a direct hit or very close pass by northern Taiwan looking increasingly likely.

Figure 4. Latest satellite image of Invest 93E (left side of image) and 92E (right side of image, close to the coast of Mexico/Central America.)

Tropical disturbances 92E and 93E a heavy rain threat to Mexico and Central America
Our three top models for predicting tropical cyclone genesis predict that an area of disturbed weather about 400 miles south of Acapulco, Mexico (Invest 93E) will develop into a tropical depression on Sunday or Monday. This system is expected to move northwards and be very near the coast close to Acapulco on Monday through Thursday, potentially bringing an extended period of dangerous flooding rains. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 90%.

Another area of disturbed weather in the Eastern Pacific along the coast near the Mexico/Guatemala border (Invest 92E) is drifting slowly to the west, and will bring heavy rains to El Salvador, southern Guatemala, and southeastern Mexico over the next few days. None of our reliable models for forecasting tropical cyclone genesis develop 92E into a tropical depression. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 30%.

Yet another area of concern is an area of low pressure that the models predict will form on Monday or Tuesday about 1000 miles southwest of the southern tip of the Baja California peninsula. Some gradual development of this system is possible later in the week while the system moves slowly northward. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the disturbance 2-day and 5-day odds of development of 0% and 20%, respectively.

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.