Watch the Fujiwhara Effect in the Northwest Pacific Ocean

Meteorologists worldwide are watching two cyclones in the Northwest Pacific begin their “dance” around each other. Tropical storm Kulap and typhoon Noru are beginning to endure a weather phenomena known as the Fujiwhara Effect.

The Fujiwhara Effect occurs when two cyclones rotate or “dance” around each other in a counter-clockwise direction (for the Northern Hemisphere). The two cyclones are actually rotating around a single point, or center, on an axis that connects the cyclone centers. Binary interaction of the cyclones can occur only if the cyclone centers are separated by a distance of roughly 1400km, or nearly 870 miles. The National Weather Service defines Fujiwhara Effect as the tendency of two nearby tropical cyclones to rotate cyclonically about each other.

Fuji July 24 Noru Kulap
Typhoon Noru (26.2N, 154.9E) and Tropical Storm Kulap (33.1N, 159.1E) dancing around each other in the Northwest Pacific just after midnight local Japan time on July 24, 2017.

The Fujiwhara effect is named after Dr. Sakhuhei Fujiwhara, who was the Chief of the Central Meteorological Bureau in Tokyo, Japan after the First World War. In 1921, he performed and studied the interaction and movements of water vortices. Dr. Fujiwhara concluded that if two water vortices spinning counter-clockwise came close enough to each other, each vortex would rotate around the other. In the atmosphere, if one vortex (tropical cyclone) is stronger than the other, eventually the smaller vortex (tropical cyclone) could get caught in the circulation of the larger one.

When the Fujiwhara Effect occurs, the intensity and track of a tropical cyclone can be greatly altered, creating a complicated and difficult forecast. In the Northwest Pacific, tropical storm Kulap will weaken and dissipate as it is engulfed by typhoon Noru over the next 24 hours.

According to Dong (1983), archived data from the National Hurricane Center portrayed the western Pacific Ocean to have a higher frequency of binary interaction than the Atlantic Ocean. During a 36 year period, 1946-1981, two spatially proximate storms averaged 1.5 annually over the western Pacific compared to .33 annually over the Atlantic. This is likely due to the Pacific having an overall higher tropical cyclone frequency compared to the Atlantic Ocean. Furthermore, Dong studied the Intertropical Convergence Zone (ITCZ) over the Pacific Ocean versus the Atlantic Ocean. He concluded the ITCZ is better defined in the Pacific basin, leading to higher tropical cyclone activity, compared to the Atlantic basin. A good majority of tropical cyclones in the Atlantic spawn from tropical waves that emerge off the West African coast.

1994 Ruth
Photo, via The Merger of Two Tropical Cyclones, of Pat and Ruth orbiting each other, approaching a distance of 200 nautical miles.

Another example of a classic Fujiwhara Effect occured during the last week of September 1994 with tropical cyclone Pat and tropical storm Ruth.

What is the Madden Julian Oscillation (MJO)?

The Madden Julian Oscillation (MJO) is an intraseasonal fluctuation that primarily initiates over the warm waters of the Indian Ocean and western Pacific.  The MJO is comprised of regions with various atmospheric features such as deep convection and atmospheric wind anomalies that propagate eastward along the ITCZ. During a convective phase of the MJO, there is an enhanced region of tropical convection and moisture resulting in above-average rainfall. The opposite is true for a suppressed convective phase. As the MJO continues propagating eastward, the monsoon trough weakens and may shift southward. East of the MJO the easterlies are strengthened, and to the west, the easterlies are weakened. Therefore the passing of positive phase MJO can affect atmospheric wind shear, which could in turn affect tropical cyclone activity.

Phillip Klotzbach studied the relationship between the MJO and the development of tropical systems in the Atlantic Basin. In his 2010 study, Klotzbach found a direct relationship between the increase in vertical wind shear and relative humidity, and enhanced tropical cyclone activity and intensification. In the convectively enhanced phase of the MJO, upper-level easterly and low-level westerly wind anomalies act together to reduce vertical wind shear. One primary ingredient for tropical cyclone development is reduced vertical wind shear. Relative humidity throughout the atmosphere is also needed for tropical development. In Camargo’s study (2009), he found that mid-level relative humidity played the most important role, compared to low-level absolute vorticity, vertical wind shear, and potential intensity in tropical cyclogenesis by the MJO. Therefore, when an eastward moving MJO and a tropical wave meet, it is possible for the tropical wave to develop into a tropical cyclone due to the enhanced atmospheric moisture and reduced vertical wind shear created by the MJO.  If a tropical cyclone already exists, its interaction with a MJO may cause the cyclone to intensify. Kingtse C. Mo discusses an increase in tropical cyclone activity over the Atlantic Basin when the convective phase of the MJO is located the Indian Ocean rather than the Pacific Ocean.July9

 

The image above represents a forecast for Outgoing Longwave Radiation (OLR) anomalies, a key detector for active MJO regions, issued by NOAA’s Climate Prediction Center (CPC). The CPC monitors and predicts climate variability and teleconnections for government, public, and private meteorological industries. Negative OLR values indicate enhanced convection or an active MJO phase (more cloud cover indicating more convective activity). Positive OLR values represent suppressed convection (less cloud cover).

The latest forecast from the ensemble mean GFS predicts an increase in OLR, possible MJO wave, across the Indian Ocean for the next two weeks. As Kingste C. Mo found in his study, there is likely an increase in tropical activity over the Atlantic Ocean when an MJO is present over the Indian Ocean.

Although Wilkens Weather is forecasting a very low chance for tropical development in the next five days, this will be a parameter worth watching this tropical season.

Major Hurricane Wilma, 11 years later

CIMSS NOAA Satellite Montage WilmaHurricane Wilma was the 21st named storm of the infamous 2005 Atlantic hurricane season. From her formation on October 15th to her demise on the 26th, Wilma would become one of the most memorable hurricanes in Atlantic basin history. As the 4th category 5 hurricane of the year, Wilma would become a monstrous bookend to an incredible, record-setting season.Read More »

Remembering 2005’s Major Hurricane Rita in the Gulf of Mexico

Hurricane Rita made landfall in extreme southwestern Louisiana on September 24th, 2005 with an intensity of 100 knots (Category 3). About 48 hours earlier, Rita was a Category 5 hurricane with a minimum pressure of 895mb, the fourth-lowest central pressure on record in the Atlantic basin. Although Rita’s history was overshadowed by Katrina, which made landfall just a few weeks earlier, the storm provided a unique challenge for both forecasters and public officials.

NASA Rita Terra satellite_20050918
NASA satellite image of Tropical Depression Eighteen over the Bahamas on Sept. 18, 2005

Rita originated as a weak tropical wave off the western coast of Africa on September 7th. The Saharan Air Layer, commonly known as Saharan Dust, and high levels of wind shear prevented the wave from producing thunderstorm activity as it moved across the tropical Atlantic. Conditions became more favorable for development later in the month as the wave reached the Bahamas. A tropical depression formed on September 17th and the system was designated as Tropical Storm Rita the following afternoon.

Rita continued to strengthen as it tracked across the Florida Straits, reaching Category 2 status by the time it reached the Gulf of Mexico on the 20th. Over the next 18 hours, the storm underwent rapid intensification over the Loop Current, becoming a Category 5 storm with an intensity of 145 knots. Rita continued to intensify and recorded an incredible 70mb drop in central pressure in a 24-hour period. At maximum intensity on September 22nd, Rita’s central pressure was estimated to be 895mb with winds near 155 knots (178 mph).

NASA Aqua satellite_20050923
NASA satellite image showing Hurricane Rita approaching the Gulf coast on Sept. 23, 2005

Thankfully for the residents of the Gulf Coast, Rita did not maintain its unprecedented strength as it pushed ashore. After moving past the Loop Current the system gradually weakened to a Category 3 before making landfall near Sabine Pass as a major hurricane. Hurricane force winds spread over 150 miles from the center while tropical storm force winds stretched as far north as the Louisiana/Arkansas border. Peak storm surge of nearly 17 feet occurred on the eastern side of Rita, causing severe flooding in several parishes in southwestern Louisiana. Heavy rainfall worsened this situation, with most of southwestern Louisiana receiving 7-10 inches, with some areas receiving over 15.

Rita continued to progress northeastward after being absorbed by a front across the central United States. That accelerated movement prevented a significant flood event in the Ohio River valley, with most rainfall totals being limited to around 2-3 inches as the remnant low raced toward the Great Lakes.

Although meteorological impacts to extreme southeastern Texas and southwestern Louisiana were unforgettable, only seven direct deaths occurred as a result of Rita in the United States. Most citizens in the southwestern Louisiana coastal areas evacuated before the worst impacts arrived, likely significantly reducing the death toll in that area.

The majority of the storm’s causalities occurred during the evacuation iWWT Hurricane Rita Wind Speed Analysisn Texas, where poor planning and heightened fears, resulting from Katrina, resulted in mass gridlock around Houston. Over 100 Texans perished due to accidents, fires, and health related issues during the evacuation. Much work has since been done to streamline the evacuation process from the Houston area, including the streamlining of the contraflow process on major highways exiting the city.

 

 

Wilkens Weather tracks 8 storms in the West Pacific this August

WWT West Pacific Tropical Summary

The West Pacific Ocean was quite active last week, with 2-3 concurrent storms. This recent tropical activity, while not unprecedented, has been above average.  Over the past several weeks, an upward Madden-Julian Oscillation phase extending across the West Pacific coupled with the existing monsoon trough.  This pattern has yielded eight named storms since August 3, the most recent being Typhoon Lionrock. Read More »

Wilkens Weather releases new tropical cyclone tracking tools for its iOS mobile app

Wilkens Weather Technologies Mobile App

Houston, USA (April 25, 2016) – Just in time for the 2016 Atlantic Hurricane season, Wilkens Weather Technologies® (WWT) has released a new version of its iOS Mobile App. The latest version contains a series of major upgrades to the app’s Interactive Weather Map, including a new Threat Profile feature which is now embedded within the global tropical cyclone tracking tools, allowing immediate threat identification of tropical systems with respect to customer assets.

“From real-time weather display to our cyclone tracking feature set, WWT effectively informs users of the impacts from an approaching tropical system,” said Ryan Fulton, program manager at Wilkens Weather Technologies. Read More »