Tropical Cyclone Ula Equivalent of Cat. 4 Hurricane

Tropical Cyclone continued to intensify steadily on Saturday and it is now the equivalent of a Category 4 hurricane on the Saffir-Simpson Scale.  At 8:00 p.m. EDT on Saturday the center of Tropical Cyclone Ula was located at latitude 19.8°S and longitude 171.4°E which put it about 400 miles (640 km) east-northeast of Noumea, New Caledonia.  Ula was moving toward the southwest at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 140 m.p.h. (225 km/h) and there were wind gusts to 165 m.p.h. (270 km/h).  The minimum surface pressure was 933 mb.

Tropical Cyclone Ula has circular eye with a diameter of 24 miles (38 km).  The eye is surrounded by a closed ring of thunderstorms.  Other spiral bands are rotating around the center of circulation.

Tropical Cyclone Ula is moving through an environment that is almost perfect for intensification.  The upper level winds are very light and there is almost no vertical wind shear.  Ula is over water where the Sea Surface Temperature (SST) is near 28°C.  It intensified quickly on Saturday and it has the potential to intensify a little more before it moves over cooler SSTs.

Tropical Cyclone Ula is moving around the western end of a subtropical ridge which is steering it toward the southwest.  That general motion is expected to continue for another 12 to 24 hours.  As Ula reaches the western end of the ridge it will start moving more toward the south.  Eventually the mid-latitude westerlies will start to steer Ula toward the southeast.

On its anticipated track Tropical Cyclone Ula could pass near the extreme southeastern islands of Vanuatu.  The greatest risk is to Aneityum and Futuna.  Ula could also bring wind and rain to Tanna, Aniwa, and Erromango.  The core with the strongest winds should pass southeast of Vanuatu, but Ula could bring wind and rain to some of those islands.  The center of Ula is expected to pass east of New Caledonia early next week, but it could also bring wind and rain to the Iles Loyaute.

Tropical Cyclone Ula Intensifies Rapidly, Threatens Vanuatu

Tropical Cyclone Ula intensified rapidly on Friday as it started to move toward Vanuatu.  At 4:00 p.m. EDT on Friday the center of Tropical Cyclone Ula was located at latitude 18.7°S and longitude 173.5°E which put it about 545 miles (880 km) east-northeast of Noumea, New Caledonia.  Ula was moving toward the southwest at 3 m.p.h. (5 km/h).  The maximum sustained wind speed was 95 m.p.h, (155 km/h) and there were wind gusts to 115 m.p.h. (185 km/h).  The minimum surface pressure was 963 mb.

Tropical Cyclone Ula intensified rapidly on Friday because it was in a very favorable environment.  Satellite images showed that there is a 15 mile (24 km) wide eye at the center of Ula.  Additional spiral bands are rotating outside the core of the tropical cyclone.  Ula has a very symmetrical structure.  Thunderstorms in the core of Ula are creating upper level divergence, especially to the west of the center of circulation.

Tropical Cyclone Ula is in an environment favorable for further intensification.  It is over water where the Sea Surface Temperature is near 28°C.  An upper level ridge to the east of Ula is producing northeasterly winds over the top of the tropical cyclone.  However, the vertical wind shear is only modest and further intensification is possible.  Tropical Cyclone Ula could become the equivalent of a major hurricane during the weekend.

A subtropical ridge east of Ula is starting to steer the tropical cyclone toward the southwest.  That general motion is expected to continue for the next several days.  On its anticipated track Tropical Cyclone Ula could approach the southern islands of Vanuatu in about 48 hours.  It could be a very strong tropical cyclone when it nears those islands.

Tropical Cyclone Ula Intensifies, Could Threaten Vanuatu

Tropical Cyclone Ula moved into a more favorable environment and it intensified on Thursday.  At 4:00 p.m. EDT on Thursday the center of Tropical Cyclone Ula was located at latitude 18.7°S and longitude 174.4°E which put it about 260 miles (420 km) west of Suva, Fiji.  Ula was moving toward the northwest at 3 m.p.h. (5 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 982 mb.

Tropical Cyclone Ula has been moving slowly equatorward this week and it is now over slightly warmer Sea Surface Temperatures (SSTs).  Ula has extracted additional energy from the warmer water and the strength of thunderstorms near the core of the tropical cyclone increased.  The structure of the circulation is more symmetrical and an eyewall may be forming around the center of Ula.  The thunderstorms are also generating more upper level divergence, especially to the west of the center of the tropical cyclone.

Tropical Cyclone Ula is once again in a region that is favorable for intensification.  It is back over water where the SSTs are near 28°C.  An upper level ridge east of Ula is generating northeasterly winds over the top of the tropical cyclone, but the vertical wind shear is modest.  Tropical cyclone is likely to intensify further during the next 24 hours and it could become the equivalent of a hurricane on Friday.

Ula has been moving slowly northwest around the western end of a subtropical ridge.  The ridge is forecast to slowly strengthen during the next few days.  As the ridge strengthens it will start to steer Ula more toward the west.  On its anticipated track Tropical Cyclone Ula could move toward Vanuatu.

Strong Low Spins Up Off Southeast Coast

A strong non-tropical low pressure system spun up off the Southeast Coast of the U.S. on Thursday and there is some possibility that it could eventually develop subtropical or tropical characteristics.   At 4:00 p.m. EST on Thursday the low pressure system was centered near latitude 29.0°N and longitude 74.0°W which put it about 425 miles (685 km) west-southwest of Bermuda.  The low was moving toward the east-northeast at 18 m.p.h. (29 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 994 mb.

The low pressure system exhibits the structure of an occluded extratropical cyclone.  An occluded front coils away from the low until it splits into a warm front and a cold front.  Drier air is being pulled around the western and southern sides of the low and a dry slot has formed in the southeastern quadrant of the storm.  However, upper level divergence is pumping mass away from the center of the low and the surface pressure decreased quickly on Thursday afternoon.

The low is in an environment that is not favorable for the classical scenario of formation of a tropical cyclone.  It is moving over water where the Sea Surface Temperature (SST) is near 25°C and strong upper level winds are creating significant vertical wind shear.  However, research has shown that it is possible to get a transition to a subtropical or tropical cyclone over cooler SSTs, when a low pressure system moves into an area where the wind shear is less.

A trough over the southeastern U.S. is steering the low pressure system toward the east-northeast and that general motion is expected to continue during the next day or two.  An upper level ridge is forecast to move north of the low pressure system in a couple of days.  The upper level ridge is expected to steer the low pressure system toward the east-southeast early next week.

If the low pressure system takes the expected track, it could eventually move over slightly warmer SSTs and into an area where there is less vertical wind shear.  The more favorable environment could cause the structure of the low to change into a more subtropical or tropical form.  The National Hurricane Center is giving the low a 10% chance of transitioning into a subtropical cyclone during the next 48 hours and a 30% chance that it makes that transition during the next five 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.

Tropical Cyclone Ula Bringing Strong Wind to SE Fiji

Tropical Cyclone Ula is bringing strong winds, heavy rain and high surf to the extreme southeastern islands of Fiji.  At 4:00 p.m. EST on Saturday the center of Tropical Cyclone Ula was located at latitude 19.4°S and longitude 178.0°W which put it about 265 miles ( 430 km) east-southeast of Suva, Fiji.  Ula was moving toward the southwest at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 105 m.p.h. (170 km/h) and there were wind gusts to 125 m.p.h. (205 km/h).  The minimum surface pressure was 961 mb.  Tropical Cyclone Ula was the equivalent of a Category 2 hurricane on the Saffir-Simpson Scale.

The inner core structure of Tropical Cyclone Ula changed on Saturday and it may have gone through an eyewall replacement cycle.  Ula started the day with a small pinhole eye, but recent visible satellite imagery indicates that it has a larger, symmetrical eye.  Even though the inner core structure has changed, Tropical Cyclone Ula maintained its intensity.  The structure of Ula is still symmetrical, but most of the stronger thunderstorms are south and west of the center of circulation.

Tropical Cyclone Ula remains in an environment that is favorable for intensification.  It is over water where the Sea Surface Temperature (SST) is near 28°C.  The upper level winds are light and there is not much vertical wind shear.  The favorable environment could allow Ula to maintain its intensity for another 12 to 24 hours.  After that time the tropical cyclone will move into an area where the SSTs are cooler and the upper level winds are stronger.  Cooler water and more vertical wind shear will cause Tropical Cyclone Ula to weaken.

A subtropical ridge is steering Tropical Cyclone Ula toward the southwest.  Ula is nearing the western end of the ridge and it is likely to turn more toward the south in a day or two.  The center of Tropical Cyclone Ula is near Vatoa, Ogea Levu and Ogea Driki.  It is bringing strong winds, heavy rain and large waves to those islands.  It will move near Ono-i-lau, Tuvana-i-colo and Tuvana-i-ro during the next few hours and conditions will get worse on those islands.

Tropical Cyclone Ula Bringing Wind and Rain to Northern Tonga

Tropical Cyclone Ula is bringing wind and rain to islands in northern Tonga.  At 10:00 p.m. EST on Friday the center of Tropical Cyclone Ula was located at latitude 18.3°N and longitude 175.6°W which put it about 100 miles (160 km) north-northwest of Tongatapu, Tonga.  Ula was moving toward the west-southwest at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 115 m.p.h. (150 km/h) and there were wind gusts to 135 m.p.h. (215 km/h).  The minimum surface pressure was 959 mb.

Lupepau’u airport on Vava’u reported maximum sustained winds of 65 m.p.h. (105 km/h) and wind gusts to 100 m.p.h. (160 km/h) when the center Tropical Cyclone Ula passed north of it.  Ula also brought strong winds and heavy rain to Tafahi, Fonaulei and Toku in northern Tonga.

Tropical Cyclone Ula intensified quickly during the past few hours and a pinhole eye is visible on conventional satellite images.  The eye is surrounded by a tight ring of strong thunderstorms.  Several spiral bands are rotating around the center of Ula.  One of the primary rainbands may be wrapping around the pinhole eye and concentric eyewalls may be developing.  Thunderstorms in the core of Tropical Cyclone Ula are generating upper level divergence that is pumping out mass in all directions.

Tropical Cyclone Ula is in an environment favorable for intensification.  Ula is moving over water where the Sea Surface Temperature (SST) is near 28°C.  The upper level winds are relatively light and there is not much vertical wind shear.  Ula could intensify further during the next few hours, although an eyewall replacement cycle could cause fluctuations in intensity.  Tropical Cyclone Ula could move into an area where the upper level winds are stronger in 24 to 48 hours.  Ula will also move over cooler SSTs in several days.  The combination of more wind shear and cooler SSTs will weaken the tropical cyclone.

A subtropical ridge is steering Tropical Cyclone Ula toward the west-southwest and that general motion is expected to continue for another day or so.  After that time Ula will reach the western end of the ridge and turn more toward the south.  On its expected track Tropical Cyclone Ula could be approaching the southeastern islands of Fiji in about 24 hours.

Tropical Cyclone Ula Becomes Equivalent of Cat. 2 Hurricane South of Samoa

Tropical Cyclone Ula intensified quickly Wednesday into the equivalent of a Category 2 hurricane on the Saffir-Simpson Scale.  At 4:00 p.m. EST on Wednesday the center of Tropical Cyclone Ula was located at latitude 16.3°N and longitude 170.4°W which put it about 135 miles (220 km/h) south-southeast of Pago Pago, Samoa.  Ula was moving toward the southwest at 5 m.p.h. (8 km/h).  The maximum sustained wind speed was 105 m.p.h. (170 km/h) and there were wind gusts to 125 m.p.h. (205 km/h).  The minimum surface pressure was 961 mb.

Tropical Cyclone Ula has a small, well organized inner core.  An eye has appeared intermittently on satellite imagery.  Thunderstorms near the core are generating upper level divergence which is pumping out mass and allowing the surface pressure to decrease.

Tropical Cyclone Ula is moving through an environment favorable for intensification.  It is over water where the Sea Surface Temperature is near 28.5°C.  The upper level winds are not very strong and there is not much vertical wind shear.  Ula could intensify a little more during the next 24 hours.

A subtropical ridge is steering Tropical Cyclone Ula toward the southwest and a general west-southwesterly motion is expected to continue during the next several days.  Ula is centered between Samoa, Niue and Tonga.  On its anticipated track Tropical Cyclone Ula will approach Tonga in about 24 hours.  It could be approaching Fiji in about three days.  Tropical Cyclone Ula is capable of bringing strong winds, high surf and heavy rain to the islands in its path.

Tropical Depression 09C Forms Near Equator

Sufficient evidence of a surface center of circulation within a broad area of thunderstorms near the Equator prompted the Central Pacific Hurricane Center to classify the system as Tropical Depression 09C.  At 10:00 p.m. EST on Wednesday the center of Tropical Depression 09C (TD09C) was located at latitude 2.8°N and longitude 177.8°W which put it about 1850 miles (2975 km) southwest of Honolulu, Hawaii.  TD09C was moving toward the west-northwest at 8 m.p.h.  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1001 mb.

The circulation of Tropical Depression 09C is not particularly well organized and there may be multiple small centers inside the larger circulation of the system.  One small center of circulation is near a cluster of thunderstorms in the northern half of the circulation and that center is currently being designated as the center of TD09C.  Another circulation center is near latitude 1.0°N and longitude 174.6°W, but there are no thunderstorms near that center.  The main area of thunderstorms is north of the official center of circulation.  There are a few partial spiral bands northeast of the center of the depression.

The environment around TD09C is only marginal for intensification.  The depression is moving over water where the Sea Surface Temperatures are near 30°C.  So, there is plenty of energy in the upper ocean to support intensification.  However, a strong upper level ridge east of TD09C is generating strong southeasterly winds over the top of the depression.  The strong vertical wind shear is contributing to the poor organization of TD09C.  The wind shear is likely to inhibit intensification during the next several days.

A subtropical ridge east of TD09C is expected to steer the depression slowly toward the west-northwest during the next few days.  The actual track of TD09C could be somewhat erratic, especially if some of the small centers of circulation dissipate and additional centers form in clusters of thunderstorms that develop.  On its anticipated track Tropical Depression 09C could approach Tarawa in about three days and it could be approaching the Marshall Islands this weekend.

The most remarkable thing about Tropical Depression 09C is that is developed so close to the Equator.  Conventional wisdom often says that tropical cyclones cannot form near the Equator because the Coriolis effect is too small.  However, although tropical cyclones are rare near the Equator, Tropical Depression 09C is another example that they can form in that region.

Tropical Cyclone Ula Forms East of Samoa

A well-defined center of circulation consolidated within a very large area of thunderstorms straddling the Equator near the International Date Line and the system was classified as Tropical Cyclone Ula (06P).  At 5:00 a.m. EST on Wednesday the center of Tropical Cyclone Ula was located at latitude 12.5°S and longitude 166.6°W which put it about 325 miles (525 km) east-northeast of Pago Pago, Samoa.  Ula was moving toward the south-southeast at 15 m.p.h. (24 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 991 mb.

Thunderstorms in a spiral rainband are wrapping around the center of circulation and microwave satellite imagery has suggested that an eye may be forming in Tropical Cyclone Ula.  Additional spiral bands are developing in the outer portion of the circulation.  The thunderstorms near the center of circulation are generating upper level divergence which is pumping out mass, especially to the east of the center of Ula.

Tropical Cyclone Ula is in an environment that is favorable for intensification.  It is over water where the Sea Surface Temperatures are between 28°C and 29°C.  The upper level winds are light and there is not much vertical wind shear.  Ula is likely to continue to intensify as the core of the circulation consolidates and it could become the equivalent of a hurricane within 24 to 36 hours.

Ula is currently being steered to the south-southeast by a subtropical ridge which is located east of the tropical cyclone.  The ridge is expected to intensify and extend westward.  If it does so, then the building ridge will cause Tropical Cyclone Ula to turn toward the southwest.  On its anticipated track the center of Tropical Cyclone could pass south of Samoa in 24 to 48 hours and it could approach Fiji in four or five days.

Tropical Cyclone Ula could bring strong winds and heavy rain to any island it passes near.