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 Public Advisory Edit

TROPICAL STORM CHAN-HOM PUBLIC ADVISORY NUMBER 1

WIKI-HURRICANES FORECASTING CENTER

12:00 PM JST TUE JUN 30 2015

...A NEW TROPICAL STORM FORMS IN THE WEST PACIFIC...

SUMMARY OF 12:00 PM JST...03:00 UTC...INFORMATION

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LOCATION...9.2N 161.1E

CENTER POSITION CONFIDENCE: AVERAGE

ABOUT 255 MI...410 KM NE OF PALIKIR, MICRONESIA

MAXIMUM SUSTAINED WINDS...35 KT...40 MPH...65 KM/H

MINIMUM BAROMETRIC PRESSURE...1004 MB...29.65 INCHES

PRESENT MOVEMENT...WNW OR 295 DEGREES AT 2 KT...2 MPH...4 KM/H

DISCUSSION AND 48-HOUR OUTLOOK

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At 12:00 pm JST, the center of newly-designated Tropical Storm Chan-Hom was situated near 9.2N 161.1E, or about 255 miles (410 km) northeast of Palikir, Micronesia. Maximum sustained winds were 35 knots (40 mph, 65 km/h), with higher gusts. The minimum barometric pressure was 1004 mb (29.65 inHg), and the cyclone was tracking slowly west-northwestward at 2 kt (2 mph, 4 km/h). Atmospheric conditions are expected to be favorable for further development of the system over the coming days as moves across the open West Pacific.

NEXT ADVISORY

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Next complete advisory at 6:00 pm JST.

$$

Forecaster TAWX14

Discussion Edit

TROPICAL STORM CHAN-HOM DISCUSSION NUMBER 1

WIKI-HURRICANES FORECASTING CENTER

12:00 PM JST TUE JUN 30 2015

The area of low pressure located a few hundred miles northeast of Micronesia has acquired sufficient organization to be declared a tropical cyclone. Satellite animations reveal the system is characterized with an organized convective mass and expanding upper-level outflow. The low-level circulation, which was previously exposed this afternoon, has become obscured on the eastern side of the irregular central dense overcast. Although the 2332z satellite intensity estimates from SAB and JTWC were T1.5/25kt and T1.0/25kt, respectively, a 2317z ASCAT MetOp-B descending pass sampled a large region of 30kt winds and a few 35kt barbs. Given that, the documented conservative bias with the instrument, and the improving satellite presentation, the initial intensity has been set at 35kt, and advisories have begun on Tropical Storm Chan-Hom.

The environment over the coming days is expected to be generally favorable for the newly-designated tropical storm. Maps from UW-CIMSS indicate that Chan-Hom is currently undergoing a moderate 10 to 15 knots of southeasterly wind shear, acting to weight a majority of the associated convective activity on the western semicircle. However, over the coming days, global model guidance is in agreement that anticyclonic flow will develop aloft. This flow will be exemplified by a northward-moving upper-level low to the cyclone's northeast which should provide an excellent poleward outflow channel. Chan-Hom is currently progressing over ocean temperatures around 29C and ocean heat content near 75 kJ/cm^2, but both of these parameters are expected to become even more favorable over the coming days. In addition, water vapor animations indicate that the atmosphere surrounding the tropical storm is sufficiently moist as to not preclude intensification. All of these factors favor steady strengthening over the coming days, and the official forecast indicates the cyclone becoming a typhoon by 96 hours, although some guidance indicates it may occur sooner. One factor that needs to be monitored is Chan-Hom's interaction with a developing area of low pressure, which has a high likelihood of becoming a tropical cyclone over the next few days, to the cyclone's west.

The initial motion is 295/2. The cyclone is currently being steered slowly west-northwest by a 591dm ridge over the subtropical West Pacific, and this trajectory is expected to remain unchanged over the next 96 hours as Chan-Hom rounds the southern periphery of the anticyclone. Thereafter, an upper-level trough is forecast to dig into Japan and erode the western side of the mid-level ridge, acting to force the tropical storm on a northwestward course. Outside the forecast period, there are indications that the ridge will once again intensify and steer Chan-Hom on a more west-northwest motion. Given the current forecast track, the cyclone appears to be a substantial threat to the southern Mariana Islands, and residents there should monitor the progress of Chan-Hom closely.

INIT 30/0300Z 9.2N 161.1E 35 KT 40 MPH

12H 30/1200Z 9.5N 160.5E 40 KT 45 MPH

24H 01/0000Z 9.8N 159.9E 45 KT 50 MPH

36H 01/1200Z 10.4N 158.1E 50 KT 60 MPH

48H 02/0000Z 10.8N 155.5E 55 KT 65 MPH

72H 03/0000Z 11.2N 148.8E 60 KT 70 MPH

96H 04/0000Z 12.1N 146.9E 70 KT 80 MPH

120H 05/0000Z 13.3N 146.1E 85 KT 100 MPH

$$

Forecaster TAWX14

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