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Public advisoryEdit

TROPICAL STORM CHAN-HOM PUBLIC ADVISORY NUMBER 13

WIKI-HURRICANES FORECASTING CENTER

12:00 PM JST FRI JUL 03 2015

...CHAN-HOM STRUGGLING SOUTHEAST OF GUAM... ...LIKELY TO RE-INTENSIFY...

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

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LOCATION...10.3N 148.5E

CENTER POSITION CONFIDENCE: HIGH

ABOUT 335 MI...540 KM SE OF HAGATNA, GUAM

MAXIMUM SUSTAINED WINDS...55 KT...65 MPH...100 KM/H

MINIMUM BAROMETRIC PRESSURE...988 MB...29.18 INCHES

PRESENT MOVEMENT...NE AT 2 KT...3 MPH...6 KM/H

DISCUSSION AND 48-HOUR OUTLOOK

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At 12:00 pm JST, the center of recently-downgraded Tropical Storm Chan-Hom was situated near 10.3N, 148.5E, or about 335 miles (540 km) southeast of Hagatna, Guam. Maximum sustained winds were 55 knots (65 mph, 100 km/h), with higher gusts. The minimum barometric pressure was 988 millibars (hPa; 29.18 inHg), and the cyclone was tracking northeast at 2 knots (3 mph, 6 km/h). Although weakening has taken place over the past few hours, environmental conditions are expected to become more favorable for significant strengthening over the coming days. Residents living in the Mariana Islands should take precautions to protect life and property now.

NEXT ADVISORY

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Next complete advisory at 6:00 pm JST.

$$

Forecaster TAWX14

DiscussionEdit

TROPICAL STORM CHAN-HOM DISCUSSION NUMBER 13

WIKI-HURRICANES FORECASTING CENTER

12:00 PM JST FRI JUL 03 2015

After undergoing a period of quick intensification late last night into this morning, Chan-hom has hit a brick wall this evening. A microwave pass at 2134z indicated that the low-level circulation of the system was becoming dislocated from its associated convective activity. Since that time, the center has become completely exposed on conventional satellite imagery. Recent satellite intensity estimates were T3.5/55kt from both JTWC and SAB; the raw estimate from UW-CIMSS ADT, which is most useful in situations where cyclones change abruptly in intensity, had plummeted to T2.2/32kt. Under the assumption that Chan-hom has not completely fallen apart this evening, the initial intensity is lowered to a potentially generous 55kt.

Maps from UW-CIMSS indicate that Chan-hom continues to undergo northeasterly wind shear in the range of 20 knots. This shear appears to be originating from an upper-level low a short distance to the cyclone's north and east. However, over the coming days, this feature is expected to drift northwesterly while simultaneously weaken. This should allow for anticyclonic flow aloft to develop and lower shear atop Tropical Storm Chan-hom. The tricky portion of the forecast enters the picture when deciphering exactly when these unfavorable upper-level winds will relent. Recent runs of the GFS and HWRF suggest that Chan-hom will maintain intensity or even weaken further over the next 24 hours and weaken intensifying thereafter, whereas the ECMWF indicates slow strengthening over the next day and quicker intensification thereafter. Given recent developments, the updated intensity forecast is closest to the GFS and HWRF runs, indicating slight weakening over the next 24 hours followed by steady and then rapid intensification thereafter.

Although the cyclone has not moved much today, the initial motion appears to be slowly toward the northeast. A mid-level disturbance to the Chan-hom's north, which was not forecast well by global models, has allowed for a weakness in the subtropical ridge to the system's north to form. This break will persist for another 24 hours or so, and a general northward track is expected during that time. After that time, a series of shortwave troughs across Japan and surrounding regions is expected to erode the western edge of the subtropical ridge and allow Chan-hom to track generally northwestward. Model guidance has shifted farther south compared to the previous advisory package, and the updated WHFC track follows suit. On its current projected path, Chan-hom is expected to cross the southern and central Mariana Islands as a typhoon, and residents there should be taking precautions accordingly.

INIT 03/0300Z 10.3N 148.5E 55 KT 65 MPH

12H 03/1200Z 10.5N 148.0E 50 KT 60 MPH

24H 04/0000Z 10.9N 147.2E 50 KT 60 MPH

36H 04/1200Z 12.3N 145.8E 60 KT 70 MPH

48H 05/0000Z 14.1N 144.9E 75 KT 85 MPH

72H 06/0000Z 16.5N 142.1E 90 KT 105 MPH

96H 07/0000Z 19.7N 138.0E 115 KT 130 MPH

120H 08/0000Z 22.7N 133.6E 130 KT 150 MPH

$$

Forecaster TAWX14

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