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Public advisoryEdit

TROPICAL STORM CHAN-HOM PUBLIC ADVISORY NUMBER 8

WIKI-HURRICANES FORECASTING CENTER

6:00 AM JST THU JUL 02 2015

...CHAN-HOM INTENSIFYING..

SUMMARY OF 6:00 AM JST...21:00 UTC...INFORMATION

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LOCATION...11.0N, 154.5E

CENTER POSITION CONFIDENCE: HIGH

ABOUT 350 MI...560KM NW OF PALIKIR, MICRONESIA

MAXIMUM SUSTAINED WINDS...50 KT...60 MPH...95 KM/H

MINIMUM BAROMETRIC PRESSURE...996 MB...29.40 INCHES

PRESENT MOVEMENT...WNW AT 15 KT...18 MPH...27 KM/H

DISCUSSION AND 48-HOUR OUTLOOK

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At 6:00 am JST, the center of Tropical Storm Chan-Hom was situated near 11.0N, 155.2E, or about 350 miles (50 kilometers) northwest of Palikir, Micronesia. Maximum sustained winds were 50 knots (60 mph, 95 km/h), with higher gusts. The minimum barometric pressure was 997 millibars (hPa; 29.44 inHg), and the cyclone was tracking west at 15 knots (18 mph, 27 km/h). Some strengthening is possible as the cyclone tracks further westward or west-northwestward. A typhoon is possible tomorrow.

NEXT ADVISORY

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Next complete advisory at 12:00 pm JST.

$$

Forecaster YE

DiscussionEdit

TROPICAL STORM CHAN-HOM DISCUSSION NUMBER 8

WIKI-HURRICANES FORECASTING CENTER

6:00 AM JST THU JUL 02 2015

Since the issuance of the previous advisory package, there has been little change in structure for Chan-hom. Deep convection is displaced to the northwest, although the ball of convection is well-organized, indicating that 15-25 knt shear is bothering the system. While the convection has continued to become more LLC-centric, intensity estimates remain unchanged. The JTWC and SAB support a T3.0/45 knt, while CI values from CIMSS-ADT are at T3.5/55 knts. The JMA seems to have awarded the system a T3.0, which on their scae, corresponds to 51 knts 10 min, which would yield an intensity of 55-60 knts 1-min. CIMSS AMSU pass from last night supported an intensity off 44 knts. A CIMSS SSMIS pass also supported 44 knts. JTWC ADT (version 8.1.4) supported an intensity of 3.7/57 knts while JMA ADT supports 3.8/61 ktns, with raw and adjusted values of 4.0/65 knts. Even when placing less weight towards the less reliable objective T-numbers, an intensity of 50 is not unreasonable.

Moderate wind shear could inhibit much intensification in the short-term. However, after 24 hours, steady possible rapid deepening is expected, although this not show quite yet due to uncertainty on how fast the shear will relax, and how it will interact with the two developing areas of low pressure to the southwest and one to east. By day 4 to dat 5, conditions are expected to become even more favorable west of the Mariana Islands, and several models, including the HWRF, GFS, and ECMWF IFS, increase Chan-hom's pace of intensification during that time. However, an upper trough to its north could cause to inherit some dry air, which models aren't the greatest at depicting. Furthermore, there is still some spread in the intensity guidance, with the JMA and CMC not too aggressive. Then, again both models have very coarse public data and are low-res and don't have the skill that other models have. In all, the new advisory package has been raised considerably than the previous. The 6z and 12z GFS and 12z ECMWF low-res has this at 927, 938 mbar, and 939 mbart low-res by day 5. As such, the new intensity forecast brings the storm to 120 knts, compared to 105 knts from the previous package.

Assuming that the 15z center fix is adjusted, as the SAB estimate was a bit east of the WHFC one, Chan-hom has accelerated westward, which has largely been a byproduct of lessening shear allowing the low level center of circulation to gravitate towards the convective mass that had previously been well west of the center. Overall, there is little spread in the guidance over the next several days. Chan-hom's motion over the next two days will largely continue to be westward as a result of a strong subtropical ridge to its north. Chan-hom is expected to interact with a developing area of low pressure to the southwest today, and will likely end with the developing system merging with Chan-hom. This interaction should tug Chan-hom slightly southwest, which all models have been indicating. An upper-level trough is expected to erode the western periphery of the subtropical ridge, forcing Chan-hom towards the northwest. The WHFC forecast track has remained largely unchanged as these parameters have mostly remained constant. This path will take it into the southern Mariana Islands early next week, and interests in the area should closely monitor this system. The new track has been shifted a little north, in accordance with latest models, but remains on the southern side of the envelope.

INIT 01/2100Z 11.0N 154.5E 50 KT 60 MPH

12H 02/0600Z 11.2N 153.1E 50 KT 60 MPH

24H 02/1800Z 11.4N 150.6E 55 KT 65 MPH

36H 03/0600Z 11.9N 148.1E 65 KT 75 MPH

48H 03/1800Z 12.6N 145.8E 70 KT 80 MPH

72H 04/1800Z 14.1N 144.6E 85 KT 100 MPH

96H 05/1800Z 16.7N 143.0E 100 KT 115 MPH

120H 06/1800Z 19.4N 139.0E 120 KT 140 MPH

$$

Forecaster YE

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