Tag Archives: CP01

Hurricane Walaka Rapidly Intensifies to Category 5

Hurricane Walaka rapidly intensified to Category 5 on the Saffir-Simpson Scale on Monday.  At 11:00 p.m. EDT on Monday the center of Hurricane Walaka was located at latitude 13.2°N and longitude 169.8°W which put it about 240 miles (390 km) south of Johnston Atoll.  Walaka was moving toward the northwest at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 160 m.p.h. (260 km/h) and there were wind gusts to 195 m.p.h. (315 km/h).  The minimum surface pressure was 920 mb.

A Hurricane Warning is in effect for Johnston Atoll.  A Hurricane Watch is in effect for the Papahanaumokuakea Marine National Monument from Nihoa to French Frigate Shoals to Maro Reef.

The circulation of Hurricane Walaka is very well organized,  There is a circular eye at the center of Walaka.  The eye is surrounded by a ring of strong thunderstorms and the strongest winds were occurring in that ring of storms.  Several bands of showers and thunderstorms were revolving around the core of Hurricane Walaka.  Storms near the core were generating strong upper level divergence which was pumping mass away from the hurricane in all directions.

Winds to hurricane force extended out about 50 miles (80 km) from the center of Hurricane Walaka.  Winds to tropical storm force extended out about 185 miles (300 km) from the center of circulation.  The Hurricane Intensity Index (HII) for Hurricane Walaka was 35.0.  The Hurricane Size Index (HSI) was 16.4 and the Hurricane Wind Intensity Size Index (HWISI) was 51.4.

Hurricane Walaka will remain in an environment very favorable for strong hurricanes for several more days.  Walaka will move over water where the Sea Surface Temperature is near 30°C.  It will move through a region where the upper level winds will be weak and there will be little vertical wind shear.  If a rainband wraps around the existing eye and eyewall, then an eyewall replacement cycle could cause Hurricane Walaka to weaken.  In several days Walaka will move into an area where the upper level winds are stronger and the vertical wind shear will increase.  Hurricane Walaka will weaken more quickly when the shear increases.

Hurricane Walaka is moving around the western end of a subtropical high pressure system.  The high pressure system will steer Walaka toward the north during the next several days.  On its anticipated track Hurricane Walaka will pass near Johnston Atoll on Tuesday.

Tropical Storm Walaka Forms South of Hawaii

Tropical Storm Walaka formed south of Hawaii on Saturday afternoon.  At 5:00 p.m. EDT on Saturday the center of Tropical Storm Walaka was located at latitude 11.5°N and longitude 159.1°W which put it about 680 miles (1095 km) south of Honolulu, Hawaii.  Walaka was moving toward the west at 15 m.p.h. (24 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1005 mb.

A distinct low level center of circulation formed within an area of thunderstorms south of Hawaii on Saturday and the Central Pacific Hurricane Center designated the system as Tropical Storm Walaka.  The circulation around Walaka was still organizing.  Most of the thunderstorms were developing in bands south and east of the center of circulation.  Bands north and west of the center consisted primarily of showers and lower clouds.  Storms south and east of the center were beginning to generate upper level divergence which was pumping mass away from the tropical storm.

Tropical Storm Walaka will be moving through an environment that will be favorable for intensification.  Walaka will move over water where the Sea Surface Temperature is near 29°C.  It will move through an area where the upper level winds are weak and there will be little vertical wind shear.  Tropical Storm Walaka will strengthen into a hurricane and it could intensify rapidly once the inner core is well organized around an eye.

Tropical Storm Walaka will move south of a subtropical high pressure system over the Central Pacific Ocean during the next two or three days.  The ridge will steer Walaka in a general westward direction.  On its anticipated track Tropical Storm Walaka will remain south of Hawaii.

Hurricane Pali Weakens As It Nears the Equator

Hurricane Pali weakened quickly on Wednesday as it moved closer to the Equator and it is now classified as a tropical storm.  At 10:00 p.m. EST on Wednesday the center of Tropical Storm Pali was located at latitude 2.7°N and longitude 172.2°W which put it about 330 miles (530 km) east-northeast of Howland Island.  Pali was moving toward the south-southwest at 9 m.p.h. (17 km/h).  The maximum sustained wind speed was 65 m.p.h. (105 km/h) and there were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 993 mb.

As Hurricane Pali moved closer to the Equator, it moved into an area of strong vertical wind shear and weakened.  A large area of thunderstorms east-northeast of Samoa could be consolidating into a new tropical cyclone.  That area of thunderstorms is generating a lot of upper level divergence which is spreading across the Equator as strong upper level winds from the south.  Those upper level winds created strong vertical wind shear over Pali as the hurricane moved south on Wednesday.  The wind shear pushed the upper portion of Tropical Storm Pali toward the north and disrupted the vertical integrity of Pali’s circulation.  The lack of vertical integrity resulted in a significant decrease in the surface wind speed on Wednesday.

The environment around Tropical Storm Pali will be unfavorable for intensification for the next several days.  The vertical wind shear will continue and it could increase if a tropical cyclone develops east of Samoa.  Tropical Storm Pali is expected to continue to weaken on Thursday.  However, if the surface circulation remains intact for another 48 hours, the wind shear could decrease during the weekend.  The Sea Surface Temperature is near 30°C and so there is sufficient energy to support intensification, if the upper level winds decrease.  If there is still a surface circulation on Saturday, then it could begin to reorganize and get stronger.  Alternatively, if the wind shear gets stronger, Tropical Storm Pali could dissipate over the weekend.

A subtropical ridge to the northwest of Pali is steering the tropical storm toward the south.  As Pali weakens, the low level circulation will be steered more by winds closer to the surface.  Those winds are blowing from the east and Tropical Storm Pali or its remnants are expected to move toward the west during the next few days.

Pali Intensifies into Rare January Hurricane

Tropical Storm Pali intensified steadily on Monday and it has become a rare January hurricane over the Central Pacific Ocean.  At 10:00 p.m. EST on Monday the center of Hurricane Pali was located at latitude 8.1°N and longitude 171.9°W which put it about 1305 miles (2100 km) southwest of Honolulu, Hawaii.  Pali was moving toward the east-southeast at 6 m.p.h. (10 km/h).  The maximum sustained wind speed was 85 m.p.h. (135 km/h) and there were wind gusts to 100 m.p.h. (160 km/h).  The minimum surface pressure was 982 mb.

The structure of Hurricane Pali improved significantly on Monday.  A primary rainband wrapped all of the way around the center of circulation and became a well formed eyewall.  The eye has been clearly visible on satellite images from the past few hours.  Thunderstorms around the eye are generating upper level divergence in all directions which is pumping out mass.

Hurricane Pali is in an environment favorable for intensification.  An upper level ridge is generating light westerly winds over the top of Pali, but the vertical wind shear is modest.  Hurricane Pali is moving over water where the Sea Surface Temperatures (SSTs) are near 28°C.  Wind shear will be the primary factor that will determine intensify changes during the next 24 to 48 hours.  If the wind shear remains minimal, then Hurricane Pali will intensify further.  If the wind shear increases to the magnitude that existed during the weekend, then Pali will weaken.  The most likely scenario is for Pali to intensify during the next 12 to 24 hours, then maintain a steady state or slowly weaken during the middle of the week.  Rapid intensification could continue during the next few hours.

Hurricane Pali remains in an area where the steering currents are weak.  It could meander slowly toward the southeast or east for another day or two.  After that time a subtropical ridge could strengthen and start to steer Pali more toward the west.

Wind Shear Weakens Tropical Storm Pali

Upper level winds blowing from the east over the top of Pali weakened the tropical storm on Saturday.  At 10:00 p.m. EST on Saturday the center of Tropical Storm Pali was located at latitude 7.7°N and longitude 174.5°W which put it about 1450 miles (2335 km) southwest of Honolulu, Hawaii.  Pali was moving toward the west at 2 m.p.h. (3 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1000 mb.

A narrow upper level ridge is generating easterly winds that are blowing over the top of Tropical Storm Pali.  The vertical wind shear produced by those winds caused the structure of Pali to become asymmetrical on Saturday.  Most of the stronger thunderstorms formed west of the center of circulation.  There are rainbands east of the center, but they are not as tall as the bands in the western half of the circulation.  Occasionally, when the wind shear lessens, new thunderstorms form closer to the center of circulation.  At times the wind shear also causes the circulation to tilt toward the west with height.  Tropical Storm Pali is over water where the Sea Surface Temperature is near 28°C.  So, there is sufficient energy in the upper ocean to support intensification, if the wind shear decreases.  However, if the wind shear stays at its current magnitude, slow weakening will continue.

Tropical Storm Pali is embedded in a larger trough of low pressure.  As a result the steering winds are relatively weak.  The easterly winds are slowly pushing Pali toward the west.  That general motion is expected to continue for another day or two.  On its anticipated track Tropical Storm Pali could meander over the Central Pacific well southwest of Hawaii for a few more days.

Tropical Storm Pali Forms Southwest of Hawaii

A surface circulation organized quickly on Thursday in an area of thunderstorms southwest of Hawaii and the Central Pacific Hurricane Center designated the system as Tropical Storm Pali.  At 4:00 p.m. EDT on Thursday the center of Tropical Storm Pali was located at latitude 4.7°N and longitude 171.2°W which put it about 1450 miles (2335 km) southwest of Honolulu, Hawaii.  Pali was moving toward the north-northwest at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 1000 mb.

Several well formed spiral bands developed within a large area of thunderstorms and the system exhibited sufficient organization to be classified as a tropical storm.  Two of the inner spiral bands appear to be wrapping around the center of circulation and the inner core of Tropical Storm Pali is organizing quickly.  A partial eyewall may be forming around the southern and western sides of the center of circulation.  Thunderstorms near the core of Pali are generating upper level divergence, which is pumping out mass.

The environment surrounding Tropical Storm Pali is favorable for further intensification.  It is moving over water where the Sea Surface Temperatures are near 29°C.  An upper level ridge east of Pali is generating southeasterly winds over the top of the tropical storm, but the vertical wind shear is not too strong.  Pali is likely to intensify further during the next 24 hours.  A period of rapid intensification may be possible, if the inner core consolidates around an eye.

A subtropical ridge east of Pali is steering the tropical storm toward the north-northwest and that general motion is expected to continue.  However, the winds steering the storm are not too strong, and it may not move much during the next several days.

Although the historical record of tropical storms over the Central Pacific is relatively short, it appears that Tropical Storm Pali may have reached tropical storm intensity at a lower latitude than any other tropical storm on record did in that region.