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Public advisoryEdit

TROPICAL STORM CHAN-HOM PUBLIC ADVISORY NUMBER 18

WIKI-HURRICANES FORECASTING CENTER

06:00 PM JST SAT JUL 04 2015

...CHAN-HOM WEAKENING AND IS UGLY...

SUMMARY OF 06:00 PM JST...09:00 UTC...INFORMATION

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LOCATION...13.1N 147.6E

CENTER POSITION CONFIDENCE: HIGH

ABOUT 175 MI...280 KM SE OF HAGATNA, GUAM

MAXIMUM SUSTAINED WINDS...40 KT...45 MPH...65 KM/H

MINIMUM BAROMETRIC PRESSURE...1000 MB...29.53 INCHES

PRESENT MOVEMENT...NNE AT 8 KT...9 MPH...14 KM/H

DISCUSSION AND 48-HOUR OUTLOOK

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At 06:00 pm JST, the center of Tropical Storm Chan-Hom was situated near 13.1N, 147.6E, or about 175 miles (280 km) southeast of Hagatna, Guam. Maximum sustained winds were 40 knots (45 mph, 65 km/h), with higher gusts. The minimum barometric pressure was 1000 millibars (hPa; 29.53 inHg), and the cyclone was tracking north-northeast at 8 knots (9 mph, 14 km/h). Environmental conditions are becoming increasingly favorable, and steady to rapid intensification is expected throughout the forecast period.

NEXT ADVISORY

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Next complete advisory at 12:00 am JST.

$$

Forecaster YE

DiscussionEdit

TROPICAL STORM CHAN-HOM PUBLIC DISCUSSION NUMBER 18

WIKI-HURRICANES FORECASTING CENTER

06:00 PM JST SAT JUL 04 2015

Tropical Storm Chan-Hom is making progress. The storm is not nearly as elongated as it was even a few hours ago, and serious deep convection is forming somewhat near the center, although the cloud tops remain quite warm. While there are no indications of a core, a warm spot is trying to form on IR imagery, and there's a decent chance that a ragged eye will form later this evening. A blend of CMISS ADT CI values of 3.1/46 knts and a CI value of T2.5/35 knts from JTWC warrants lowering the intensity to 40 knots.

Conditions have become more favorable for intensification. The upperl-evle outflow is expanding to some extent, and according to the UW-CIMSS shear maps, vertical wind shear has fallen a good 10-20 knots over the past day or so. With sea surface temperatures on the order of 29-30C, plenty of ocean heat content, and sufficient mid-level moisture, steady strengthening is forecast over the next few days. However, only slow intensification is expected overt the next day or so until the cyclone finishes an inner core. Once an inner core is established, the potential for rapid intensification is high. The GFS and HWRF continue to indicate that Chan-hom will exceed the Category 5 threshold by the end of the forecast period, whereas the ECMWF only shows the system as a Category 3-equivalent at the same time. Given the fact that the ECMWF is low-res and not the best model in the deep tropics, the intensity forecast below calls for a super typhoon.

A mid-level trough has acted over the past 24 hours to weaken the 594dm mid-level ridge to the north of Chan-hom, allowing the cyclone to move northward and at times northeastward. However, over the subsequent day, this ridge is expected to re-intensify and force Chan-hom on a westward or northwestward motion. In fact, this motion may already be taking place. After 72 hours, as the system approaches the western extent of the anticyclone, the storm should turn increasingly poleward. The updated WHFC forecast is slightly farther north in the short term to account for the erratic center motion over the past day, but it is generally unchanged several days out.

INIT 04/0900Z 13.1N 147.6E 40 KT 45 MPH

12H 04/1800Z 14.6N 146.1E 45 KT 50 MPH

24H 05/0600Z 15.8N 145.1E 55 KT 65 MPH

36H 05/1800Z 16.9N 143.6E 60 KT 70 MPH

48H 06/0600Z 18.1N 141.6E 70 KT 80 MPH

72H 07/0600Z 21.3N 137.1E 105 KT 120 MPH

96H 08/0600Z 24.8N 133.0E 125 KT 145 MPH

120H 09/0600Z 27.7N 129.3E 130 KT 150 MPH

$$

Forecaster YE

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