Tag Archives: Mariana Islands

Typhoon Maria Rapidly Intensifies Into Equivalent of Major Hurricane

Typhoon Maria rapidly intensified Thursday into the equivalent of a major hurricane as it moved west of the Mariana Islands.  At 5:00 p.m. EDT on Thursday the center of Typhoon Maria was located at latitude 15.7°N and longitude 142.1°E which put it about 210 miles (340 km) northwest of Guam.  Maria was moving toward the northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 125 m.p.h. (205 km/h) and there were wind gusts to 155 m.p.h. (250 km/h).  The minimum surface pressure was 950 mb.

After striking Guam as a tropical storm on Wednesday Maria rapidly intensified into a strong typhoon on Thursday.  A circular eye was evident on satellite imagery.  The eye was surrounded by a ring of strong thunderstorms.  Several bands of showers and thunderstorms were revolving around the core of the circulation.  Storm in the core were generating strong upper level divergence which was pumping mass away from the typhoon in all directions.  Winds to typhoon force extended out about 35 miles (55 km) from the center of circulation.  Winds to tropical storm force extended out about 155 miles (250 km) from the center.

The Hurricane Intensity Index (HII) for Typhoon Maria was 23.6.  The Hurricane Size Index (HSI) was 14.1 and the Hurricane Wind Intensity Size Index (HWISI) was 37.7.

Typhoon Maria will continue to move through an environment favorable for intensification for another day or two.  Maria will move over water where the Sea Surface Temperature is near 30°C.  It will move through a region of weaker winds between an upper level low to the west and an upper level low to the east.  There will be little vertical wind shear.  Typhoon Maria is likely to intensify more on Friday and it could become the equivalent of a Category 5 hurricane on the Saffir-Simpson Scale.  An eyewall replacement cycle could occur if one of the rainbands wraps around existing eye and eyewall.  If an eyewall replacement cycle starts, it will cause Typhoon Maria to weaken at least temporarily.

Typhoon Maria was moving south of a subtropical ridge over the Western North Pacific Ocean.  The ridge was steering Maria toward the northwest.  A general motion toward the northwest is expected to continue for another day or two.  The ridge is forecast to strengthen after that time and it will steer Typhoon Maria more toward the west-northwest.  On its anticipated track Maria will pass south of Iwo To.  Typhoon Maria could approach Okinawa and the Ryukyu Islands in four or five days.

Tropical Depression 27W Forms Southeast of Pohnpei

A center of circulation formed in an area of thunderstorms southeast of Pohnpei and the system was designated Tropical Depression 27W (TD 27W).  At 10:00 p.m. EST on Monday the center of Tropical Depression 27W was located at latitude 4.7°N and longitude 162.3°E which put it about 360 miles (585 km) east-southeast of Pohnpei.  TD 27W was moving to the west at 17 m.p.h. (27 km/h).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1001 mb.

The circulation of TD 27W is still organizing.  A clearly defined low level center of circulation formed near the northern edge of an area of thunderstorms.  However, most of the stronger thunderstorms are southwest of the center.  Those storms are generating upper level divergence that is expanding south and west of the center.

Tropical Depression 27W is in an environment that favors further intensification.  It is over water where the Sea Surface Temperature is near 30°C.  An upper level ridge north of TD 27W is producing light easterly winds over the top of the depression.  The vertical wind shear is modest, and it should only slow the rate of intensification.  Intensification could be slow initially as a stronger inner core forms around the center of circulation.  Once the core of the circulation consolidates, then intensification could occur more quickly.  TD 27W could become a tropical storm within 24 to 36 hours and it could be a typhoon in three or four days.

A subtropical ridge north of TD 27W is steering the depression toward the west.  A gradual turn toward the west-northwest is expected and that general motion is expected to continue for much of the week.  On its anticipated track TD 27W could be near Pohnpei in about 24 hours and it could bring tropical storm force winds and heavy rain.  The tropical cyclone could be approaching Guam by the end of the week and it could be a typhoon by that time.

Powerful Typhoon Nangka Moving Through Northern Marianas

Powerful Typhoon Nangka is moving through the northern Mariana Islands.  At 11:00 p.m. EDT on Wednesday the center of Typhoon Nangka was located at latitude 17.2°N and longitude 146.5°E which put it about 145 miles (240 km) north-northeast of Saipan and about 45 miles (75 km) southeast of Alamagan.  Nangka was moving toward the west-northwest at 12 m.p.h.  The maximum sustained wind speed was 145 m.p.h. (235 km/h) and there were wind gusts to 170 m.p.h. (275 km/h).  Nangka is the equivalent of a Category 4 hurricane on the Saffir-Simpson Scale.  The minimum surface pressure was 929 mb.

Nangka has a very symmetrical structure and strong convection surrounds the eye.  It is over warm Sea Surface Temperatures and it could intensify further.  Upper level outflow from the eastern side of large Typhoon Chan-hom which is about 1200 miles (1940 km) west-northwest of Nangka could begin to create wind shear over the western side of Nangka.  Eyewall replacement cycles could also produce fluctuations in intensity.

A subtropical ridge is steering Nangka toward the west-northwest and that steering pattern is expected to continue for another two or three days.  On its anticipated track the core of Nangka will pass close to the islands of Guguan, Alamagan, Pagan and Agrihan.  It could bring very strong winds and heavy rain to those locations on Thursday.

Nangka Intensifies Rapidly Into a Strong Typhoon

Typhoon Nangka intensified rapidly into a strong typhoon on Monday.  At 11:00 p.m. EDT on Monday the center of Typhoon Nanga was located at latitude 13.2°N and longitude 155.0°E which put it about 670 miles (1080 km) east-southeast of Saipan.  Nangka was moving toward the west-northwest at 13 m.p.h. (21 km/h).  The maximum sustained wind speed was 110 m.p.h. (180 km/h) and there were wind gusts to 130 m.p.h. (210 km/h).  The minimum surface pressure was 952 mb.

The circulation of Typhoon Nangka is very well organized with a strong ring of thunderstorms surrounding a circular eye.  The typhoon is over an area where the Sea Surface Temperature is around 28°C to 29°C.  The upper level winds are relatively light and there appear to outflow channels to the northeast and southwest which are transporting mass away from the center of circulation.  The surface pressure is decreasing rapidly and the wind speeds are increasing quickly.  Nangka is in an environment that is very favorable for further intensification and it could become a very powerful typhoon.

A subtropical ridge is steering Nangka toward the west-northwest and that general motion is expected to continue during the next few days.  On its anticipated track Typhoon Nangka could approach the northern Mariana Islands in about 48 to 72 hours.

Tropical Storm Chan-hom Moving Toward Marianas

Tropical Storm Chan-hom has resumed a northwesterly motion and it is moving toward the Mariana Islands.  At 11:00 p.m. EDT on Friday the center of Tropical Storm Chan-hom was located at latitude 12.7°N and longitude 148.2°E which put it about 250 miles (400 km) east-southeast of Guam.  Chan-hom was moving toward the northwest at 11 m.p.h. (18 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 989 mb.  A Typhoon Watch is in effect for Guam, Rota, Tinian and Saipan.

The upper level low that produced the vertical wind shear which blew the top off Chan-hom on Thursday moved northeast and the upper level winds decreased on Friday.  A reduction in vertical wind shear allowed new thunderstorms to develop around the center of circulation and the circulation became better organized.  The thunderstorms near the center are beginning to generate upper level divergence and more spiral bands appear to be forming.  Chan-hom is over water where the Sea Surface Temperature is near 29°C.  The environment is favorable for intensification and rapid intensification is possible, if the wind shear remains modest.  Chan-hom could attain typhoon intensity before it reaches the Mariana Islands.

A subtropical ridge is steering Chan-hom toward the northwest and that ridge is expected to continue to steer it in the same general direction during the next few days.  On its anticipated track, Chan-hom could approach the Mariana Islands in about 24 hours.  The center could pass north of Guam, but it may pass near to Rota, Tinian or Saipan.  Chan-hom will bring wind and heavy rain to any islands it crosses.

Tropical Storm Nangka Forms East of Kwajalein

Another tropical storm formed over the western North Pacific when a circulation developed west of the International Dateline and was designated as Tropical Storm Nangka (11W).  At 11:00 p.m. EDT on Friday the center of Tropical Storm Nangka was located at latitude 9.9°N and longitude 169.2°E which put it about 150 miles east-northeast of Kwajalein.  Nangka was moving toward the west-northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 992 mb.

Tropical Storm Nangka is moving over water where the Sea Surface Temperature is near 30°C.  The upper level winds are light and upper level divergence is increasing.  However, there is sinking drier air north of the tropical storm and the circulation appears to be pulling some of the drier air into it.  As a result many of the stronger thunderstorms are occurring in the western half of the circulation.  The drier air could inhibit intensification in the short term.  The other favorable environmental factors are likely to produce intensification in the longer term once Nangka moves west of the drier air.

A subtropical ridge north of Nangka is expected to steer it in a west-northwesterly direction during the next few days.  On its expected track Nangka will bring wind and rain to a number of atolls in the Marshall Islands.  Nangka could approach the Mariana Islands in a few days.

Tropical Storm Chan-hom Forms East of Guam

A center of circulation developed in an area of thunderstorms on the opposite side of the Equator from Tropical Cyclone Raquel and it was designated as Tropical Storm Chan-hom on Tuesday.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Chan-hom was located at latitude 11.0°N and longitude 156.5°E which put it about 250 miles (400 km) north-northeast of Oroluk atoll and about 800 miles (1290 km) east of Guam.  Chan-hom was moving toward the west at 22 m.p.h. (35 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 993 mb.

Tropical Storm Chan-hom formed over water where the Sea Surface Temperatures (SSTs) are around 29°C to 30°C and there is plenty of energy in the upper ocean to support intensification.  An upper level ridge located north of the tropical storm is generating easterly winds over the top of the circulation.  The easterly winds are generating moderate amounts of vertical wind shear and many of the stronger thunderstorms are occurring in the western half of the circulation.  Those thunderstorms are producing strong rising motion and upper level divergence is well developed on the western side of Chan-hom.  However the upper level easterly winds are interfering with upper level divergence on the eastern side of the tropical storm.  As a result, a modest rate of intensification is expected in the short term.  If the upper level winds were to lessen, then a more rapid rate of intensification would be possible.

The upper level ridge is expected to steer Chan-hom toward the west during the next several days.  On its anticipated track Chan-hom could approach Guam in about three days.  It could be a typhoon by that time.  However, there is some divergence in the track guidance from numerical models at the end of this week and that is producing uncertainty about the future track of Chan during that time period.