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Fred Weakens after Lashing Cape Verde Islands

By: Bob Henson 4:21 PM GMT on September 01, 2015

Tropical Storm Fred, downgraded from hurricane status on Monday night, carved its way into the record books as it made the most direct hurricane strike on the Cape Verde islands in modern records. Fred has since weakened while plowing into a large batch of dry, dusty Saharan air. As of 11:00 am EDT Tuesday, Fred was located about 250 miles northwest of the islands, with top sustained winds down to 50 mph. The National Hurricane Center expects that Fred will continue to steadily weaken over the next couple of days as it moves northwestward.

At its height, Fred boasted prominent spiral banding, and microwave data revealed a well-defined eye, although it was mostly cloud-covered in visible satellite imagery. Although it appears that Fred’s center did not make a landfall on any of the islands, it came within roughly 20 miles of the northeastern island of Boa Vista and the northwestern islands of Sao Nicolau and Santo Antau, so Fred’s eyewall may have affected each of these areas. Boa Vista was on the stronger right-hand side of the storm, whereas Sao Nicolau and Santo Antau fell on the weaker left-hand side of Fred. Either way, many residents unaccustomed to extreme weather could have experienced very strong winds and heavy rain. Several weather stations on the islands did not report at the height of the storm, so our picture of what happened is still incomplete. Arlindo Lima, president of the National Civil Protection Service for the Republic of Cabo Verde (the nation’s official name in all languages since 2013) reported that Boa Visa and Sal, both north of Fred’s track, were the hardest-hit islands, with about 120 islanders displaced to a shelter. The nation’s airports were closed ahead of Fred’s arrival. Reports and photos on a Facebook page dedicated to Boa Vista suggest widespread but mostly minor damage, with trees and communication towers knocked down. There were no reports of casualties as of early Tuesday, according to an AFP update. Storm surge expert Hal Needham (Louisiana State University) was not expecting the surge from Fred to be extreme, since the hurricane had not had much time as a tropical cyclone to push large amounts of water ahead of it. The Cape Verde news site A Naca reported flooding related to Fred in the West African republic of Guinea-Bissau, with flooding and some evacuations in the capital city of Bissau. (Thanks to WU member barbamz for several of the websites above, translated via Google Translate.)

Figure 1. Official positions for Hurricane Fred, as provided by the National Hurricane Center, suggest that the hurricane wove its way around the northern Cape Verde islands without making a complete landfall, although Fred’s eyewall may have affected several islands. Image generated by WU’s Storm app for iPad.

Figure 2. MODIS image of Hurricane Fred from NASA's Terra satellite, taken at approximately 11:15 am EDT on Monda,y August 31, 2015. At the time, Fred had top sustained winds of 85 mph. Image credit: NASA.

Figure 3. “Hot towers” (orange) extending up to 52,000 feet (16.2 km) were evident near the center of intensifying Tropical Storm Fred at 0236 GMT Sunday, August 30 (10:36 pm EDT Saturday), not long after it had moved off the west coast of Africa. As NASA’s Global Precipitation Mission satellite examined the developing Fred, it found rainfall occurring at close to 128 mm (5.0 inches) per hour within the hot towers. Fast-growing Fred was designated as a tropical depression about three hours after this image was collected; it became a tropical storm at 5:00 am EDT Sunday and a hurricane at 2:00 am EDT Monday. Credit: NASA/JAXA/SSAI, Hal Pierce

Fred the record-setter
Fred’s arrival led to a “fountain of ‘firsts’,” as Capital Weather Gang put it. Among them:

--Fred was the easternmost hurricane to develop in the tropical Atlantic in NOAA’s HURDAT database, which extends back to 1851. (These records are less complete and reliable prior to the advent of satellite monitoring in the 1960s.) Fred was dubbed a hurricane at 2:00 am EDT Sunday while at 15.3°N, 22.5°W. During the record-setting 2005 Atlantic season, Hurricane Vince actually formed further east than Fred (18.9°W), but at a much higher latitude (34.1°N).

--Fred made the closest approach to a Cape Verde island of any hurricane in the HURDAT database. The only other hurricane to affect the islands, other than glancing blows from well to the south, was an unnamed 1892 storm that moved between the two clusters of islands that makes up the Republic of Cabo Verde. As Jeff Masters and I noted yesterday, independent hurricane scholar Mike Chenoweth has identified the most damaging storm known to affect the islands: an apparent hurricane on September 2, 1850 (predating the HURDAT database) that reportedly destroyed more than 600 homes and wiped out crops. See our Monday post for more details from Mike’s research.

--The Cape Verde islands were under their first-ever official hurricane warning on Monday.

--Courtesy of Fred, we now have the first satellite images ever collected of a hurricane over the Cape Verde islands.

New tropical wave expected to emerge from Africa on Thursday
A tropical wave currently over west-central Africa is expected to move off the coast of Africa on Thursday, at a location a few hundred miles southeast of the Cape Verde islands. The Tuesday morning runs of the GFS model predicted some slow development of this wave late in the week as it moves west at 15 - 20 mph towards the Lesser Antilles Islands. Our other two reliable models for predicting tropical cyclone genesis, the European and UKMET models, depicted an atmosphere with higher wind shear, and little or no development of the new tropical wave. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave the wave 2-day and 5-day odds of development of 0% and 20%, respectively.

Pacific staying busy
Several potent tropical cyclones are racking up the accumulated cyclone energy (ACE) across the Pacific, even as El Niño continues to keep the Atlantic relatively suppressed. Accumulated cyclone energy, or "ACE," is used to express the activity and destructive potential of individual tropical cyclones and entire tropical cyclone seasons. ACE is calculated as the square of the wind speed every 6 hours, and is then scaled by a factor of 10,000 for usability. For the Northern Hemisphere as a whole, the total ACE (now more than 500 units) is far ahead of any other year through August 31, according to WU contributor Phil Klotzbach (Colorado State University). The previous record-holder, 2004, had a total of 389 ACE units by this point. The record for an entire year was 853 ACE units, achieved in 1992.

Figure 4. Accumulated cyclone energy (ACE) through August 31 for each year up since reliable records began in 1971 in the Northeast Pacific. Image credit: Phil Klotzbach, Colorado State University.

Most of this year’s amazing ACE can be attributed to a number of typhoons and hurricanes in the North Pacific that have been both powerful and long-lived. From Saturday into Sunday, Hurricane Kilo, Hurricane Ignacio, and Hurricane Jimena were all at Category 4 strength--the first time since the satellite era began in the 1960s that three simultaneous Category 4 hurricanes had existed in the waters of the Eastern Pacific, east of the International Date Line. Ignacio continues to slowly decline as it heads northwest of Hawaii, while Jimena—now in its fourth day as a major hurricane—should weaken only gradually as it moves northward well east of Hawaii. A new system in the Northeast Pacific, Tropical Depression 14-E, is expected to become a minimal tropical storm at best as its heads toward Baja California.

For sheer longevity, Hurricane Kilo--which will become Typhoon Kilo when it crosses the Date Line over the next few hours--appears to be going for the gold. Today (September 1) is Kilo’s 12th day as a tropical cyclone and third day as a major hurricane. The Joint Typhoon Warning Center keeps Kilo as a major tropical cyclone for the next five days as it drifts across the open North Pacific, restrengthening from Category 3 to Category 4 levels by Day 3. Klotzbach notes that the ECMWF model keeps Kilo going as a strong tropical cyclone for at least 10 more days, possibly challenging the record of about 11 total days that Hurricane Ioke racked up as a major tropical cyclone. According to the National Hurricane Center, the longest-lived tropical cyclone in the satellite era is Hurricane/Typhoon John, which was tracked for 31 days during August and September 1994. In the Atlantic, the record-holder is 1971’s Hurricane Ginger (28 days).

Phil Klotzbach has much more on the record-setting Northern Hemisphere tropical cyclone season in a two-part Weather Underground blog entry posted on August 25 and August 28.

We’ll have our next post on Wednesday.

Bob Henson


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