Invest 95L Drenches Florida’s West Coast; Super Typhoon Soudelor Threatens Taiwan

Already reeling from days of heavy rain, the Florida coastline from Tampa to the Big Bend area got an unwelcome visitor on Sunday night in the form of Invest 95L. A well-defined swirl was evident Sunday on satellite imagery just west of Florida’s Big Bend, near the weak south end of a large upper-level low covering much of eastern North America. The National Hurricane Center began tracking the system as Invest 95L at 0000 GMT Monday, with an initial surface wind speed of 30 mph. At 8:00 am EDT Monday, NHC placed the weak center of low pressure over north central Florida. Winds were strongest offshore, with sustained westerly winds of 20 – 30 mph reported on Sunday night at several buoys in the far northeast Gulf. A gust to 42.5 mph occurred at Buoy 42036, according to The Weather Channel’s Stu Ostro. Most of the shower and thunderstorm activity associated with 95L has been on its south side, extending into parts of the Florida west coast just north of Tampa Bay.


Figure 1. Infrared image shows a disorganized 95L producing extensive rainfall across central Florida. Image credit:. NASA MSFC Earth Science Office.


Figure 2. Parts of the northwest Florida coast picked up widespread rainfall totals of 10” to 20" in the two weeks ending at 8:00 am EDT Monday, August 3, with additional rain falling later on Monday. Image credit: NOAA Advanced Hydrological Prediction Service.

As the upper low shifts east, it will gradually nudge the system northeastward across the Florida peninsula over the next day or so. Some acceleration is expected by midweek as the center finally moves away from Florida. There will be little chance for 95L to intensify much while it remains so close to land, although there is a slender possibility of some strengthening (most likely in a subtropical or hybrid mode) after 95L clears Florida, assuming it travels along the Gulf Stream. NHC gives the system only 10% odds of developing into a tropical cyclone over the next 5 days. The extremely rich moisture associated with the circulation will continue to sweep onshore, contributing to more episodes of heavy rain. A lingering frontal boundary has kept the northwest Florida coast in deep moisture with frequent rounds of showers and thunderstorms, now leading to rainfall totals that are posing serious problems. Tampa International Airport received 4.08” of rain between 6:00 and 11:00 am EDT Monday, on the heels of 3.89” observed on Saturday and 11.84” through July (most of it during the last two weeks of the month). Water rescues took place on Monday morning in Pinellas County, with evacuations ordered of at least one neighborhood near Elfers, Florida, northwest of St. Petersburg. Flash flood watches extended along the coastal counties from Tampa to the Big Bend on Monday morning, with the heaviest rains expected to shift inland later today.



Figure 3. Typhoon Soudelor inflicted mostly minor but widespread damage across Saipan. Image credit: American Red Cross, via Pacific Daily News.

Soudelor brings extensive damage to Saipan
Trees were snapped and power lines brought down across much of Saipan after a miniscule but mighty Super Typhoon Soudelor (not yet a super typhoon at that point) barrelled into the southern half of the island. At 10:54 pm local time on Sunday (8:54 am EDT Sunday), sustained winds of 54 mph and gusts to 91 were reported at Saipan International Airport, located on the south end of the island and close to the tiny south eyewall of Soudelor. Stronger winds most likely occurred in the north eyewall, where the westward motion of the storm would have added to wind speeds. Soudelor was officially classified as a Category 1 storm at this point, but its small-scale structure was virtually impossible to resolve in standard satellite imagery and the typhoon was already rapidly intensifying, so peak winds on Saipan might have been considerably stronger. The Pacific Daily News reported that about 350 people were in shelters at midday Monday, and a state of disaster has been declared. Fortunately, initial reports listed only a few minor injuries.

Part of the U.S. Commonwealth of the Northern Marianas, Saipan extends only about 12 miles from north to south, but Soudelor was even more compact than that. Just before landfall, a National Weather Service NEXRAD radar image showed the eye of Soudelor to be only about 4 nautical miles in diameter, surrounded by an miniature ring of showers and thunderstorms (see Figure 4). This is among the smallest eyes and eyewalls observed anywhere as a tropical cyclone was making landfall. According to the final hurricane-hunter reconnaisance report, 2004’s destructive Hurricane Charley had an eye diameter of 5 nm, within a larger zone of convection than Soudelor, just before making landfall in southwest Florida on August 13, 2004, at the end of a period of sudden strengthening to Category 4 strength. In the open Atlantic, the record-holder for smallest observed eye is another compact tropical cyclone, Hurricane Wilma, whose eye shrank to an amazing 2 nm in diameter while hurricane hunters were in the vicinity. Wilma was another rapidly intensifying cyclone, with peak winds jumping from 150 to 184 mph in less than six hours. (A reconniasance report from 1993’s Hurricane Emily also showed a 2-nm eye, but Emily was only at tropical storm strength and its eyewall was partially open at the time, so it does not reflect the same processes discussed above, and the report could be an error. Thanks to The Weather Channel’s Michael Lowry and Stu Ostro for these examples.)


Figure 4. The pinhole eye of Typhoon Soudelor was evident in NEXRAD radar imagery from 1229 GMT (8:29 pm local time) on August 2, as the typhoon bore down on Saipan from the east-southeast. The island extends roughly 12 miles from its southern to northern tip. Image credit: NOAA, courtesy Mike Middlebrooke, Senior Forecaster, NWS/Guam.


Figure 5. A colorized infrared image of Hurricane Wilma near its peak intensity, collected at 1245 GMT on October 19, 2005. Unlike Soudelor, Wilma had a large shield of intense convection surrounding its tiny eye, which was only 2 nm wide at its smallest. Image credit: NOAA, courtesy Stu Ostro, The Weather Channel.

Now a super typhoon, Soudelor bears close watching
Soudelor carried out a spectacular burst of intensification on Sunday, no doubt aided by its ultra-compact size, which allows for more rapid strengthening. Sustained winds rocketed from 70 mph at 0000 GMT Sunday to 135 mph at 0000 GMT Monday. During the day on Monday, Soudelor continued to impress by carrying out an eyewall replacement cycle clearly evident in 1-km-resolution imagery collected by Japan’s Himiwari-8 satellite, with the pinhole eye decaying as a much larger eye developed around it. (Here’s a pair of not-to-be-missed Himiwari-8 satellite loops from Sunday and Monday, courtesy Dan Lindsey/CIRA and Japan Meteorological Agency). The Joint Typhoon Warning Center reported peak winds of 155 mph in its 1200 GMT Monday advisory, making Soudelor a super typhoon.


Figure 6. An infrared MTSAT image of Super Typhoon Soudelor, collected at 1401 GMT on August 3. Image credit: NOAA/NESDIS.


Figure 7. Japan’s Himiwari-8 satellite captured this large-perspective view of Soudelor at 1240 GMT on August 3. The island of Taiwan is shown at top left. Image credit: CIRA and Japan Meteorological Agency

With very warm sea-surface temperatures (31°C, or 88°F) along its path and upper conditions remaining favorable, Soudelor could intensify even more by Tuesday. Models agree on a straightforward west-northwest path over the next several days, which puts the typhoon uncomfortably close to northern Taiwan by the end of the week. The latest JTWC outlook (1200 GMT Monday) has Soudelor clipping the island at Category 3 strength. Soudelor could pose a serious threat to Taiwan, where typhoons crashing against high terrain can produce some of the heaviest rainfall rates measured on Earth. Track uncertainty in the 4-5 day time range means that the entire island needs to be on alert. Soudelor will likely move on to strike the east coast of China, although its intensity at this point will be strongly influenced by its eventual trajectory over or near Taiwan.

Guillermo weakens to a tropical storm
At 5:00 am local time (11:00 am EDT) Monday, the Central Pacific Hurricane Center downgraded former Hurricane Guillermo to tropical-storm status, with peak winds of 70 mph. Located near 16.6°N and 146.1°W, Guillermo continued to move west-northwest at about 10 mph. Upper-level wind shear of about 15 knots has contributed to Guillermo’s gradual decline, and further slow weakening is expected, so Guillermo will probably be a fairly weak tropical storm by the time it nears Hawaii late Wednesday. Data from the NOAA Gulfstream IV large-scale reconnaissance mission entered last night’s 0000 GMT Monday model runs, which has resulted in an eastward nudge to Guillermo’s expected track. This further reduces the threat to Hawaii; although the track will take Guillermo on an unusual trajectory paralleling the entire island chain, most models now place Hawaii on the weaker left-hand side of Guillermo. However, only a slight westward shift would put the islands on the stronger right-hand side. In any event, dangerously large swells will affect Hawaii’s east-facing coastlines over the next several days.

Rare August cyclone in the South Pacific
One of the first storm-strength tropical cyclones, if not the first, known to occur in the South Pacific during August is making its way southward with minimal impact. At 0900 GMT, Tropical Cyclone One (not yet assigned a name) was located near 10.9°S, 172.6°E, with sustained winds of 40 mph, just above minimal tropical storm strength. Unusually warm water temperatures associated with El Niño have made the South Pacific unseasonably active. Last month produced Tropical Cyclone Raquel, which struck the Solomon Islands at hurricane strength as the only tropical cyclone on record to occur in the basin during July. Moderate wind shear and cooler sea-surface temperatures downstream are expected to keep TC1 at minimal intensity for the next couple of days. Currently drifting eastward, TC1 is expected to gradually head southward before eventually dissipating, far from any populated areas.

Pacific Northwest continues to sizzle
Seattle, Washington, and Salem, Oregon, endured their hottest month in more than 120 years of recordkeeping during July, as high pressure kept rains at bay and hot weather in control of the Pacific Northwest. WU weather historian Christopher Burt has a full report on the many records smashed in July across Oregon and Washington, which are on their way to the warmest summer on record. If there’s any upside, it’s that wildfire activity (as measured by acreage burned) is actually below average this summer over the two states, despite the tinder-dry conditions. Cliff Mass (University of Washington) explains the paradox in a recent blog post. For starters, the atmosphere is so suppressed that little of the normal “dry lightning” from low-precipitation thunderstorms is occurring, and winds are too light to kick up any fires that do happen to start. Mass also credits the rapid response of state and federal firefighters this year in snuffing out potential fire disasters.

Bob Henson