JMA has joined JTWC and upgraded 05W into a Tropical Storm--giving it the international name of 'Guchol'. TS Guchol was last located approximately 440km south southwest of Guam or about 510km east of Yap. Maximum sustained winds are at 65kph gusting to 85kph. TS Guchol is moving westward at 15kph.
Tropical Storm Warning remains in effect for Ulithi and Fais. A Tropical Storm Watch remains for Yap Island.
IR Image from NRLMRY
The storm remains weak in terms of convective activity but is slowly becoming more symmetrical in appearance. We are seeing some strong cloud tops starting to appear as well and as we have said for several days now, we are probably gonna see another burst of convective activity overnight. As it develops and becomes more 'vertically stacked' we expect Guchol to start intensifying at a more consistent pace.
The IR image also shows clouds moving into Guam. An interaction with an upper-level low is enhancing thunderstorms in the Northern Mariana Islands and could bring scattered thunderstorms in that area tonight. As of Ulithi and Fais, they will start encountering gusty winds of 30 to 50kph tonight. Squally rain showers will also begin and last throughout tomorrow. While the strongest of winds are found on the northern side, Guchol will pass very closely to these atolls that Tropical Storm-force winds are possible. Meanwhile, conditions in Yap Island will start deteriorating tomorrow afternoon (Wednesday). Guchol will pass within 100km to the north of the island so we still expect TS-force gusts by Thursday.
Tropical Storm Guchol will continue moving westward for the next 24 to 36 hours, slowly intensifying along the way. However, higher wind shear may slow down development but it should weaken by Thursday allowing Guchol to intensify. TS Guchol is expected to enter the Philippine Area of Responsibility by Thursday night and will be given the local name 'Butchoy' by PAGASA.
Computer models are somewhat split regarding Guchol's future track. Key pieces are the subtropical ridge and a trough that will develop in Northeastern China. We have to keep watching these two features as they will be important in forecast the track. Hopefully by Friday, models will have a better handling on the storm as well as these features. Intensity forecasts vary as well with a few models forecasting Guchol to be a typhoon while others keep it as a weak Tropical Storm.
Forecast Track (NOT OFFICIAL!)
Our forecast track is in the middle of the model output with the intensity forecast closer to JTWC and JMA. We expect Guchol to continue moving westward under the influence of the ridge. Again, lots of uncertainties remain but for now, we are keeping Guchol away from Luzon as it should start turning more to the north by Friday. Nevertheless, a slight shift in any of these scenarios could bring Guchol much closer to Luzon so be sure to keep checking our site for the latest information. As for intensity, we expect Guchol to become a typhoon by Thursday. Unless wind shear weakens dramatically, we are keeping Guchol as a Category 1 Typhoon. However, if conditions continue to improve, the storm may undergo rapid intensification--as what JTWC is suggesting--and it could end up much stronger than what we have right now.
Long-range forecast shows a wide cone that affects anywhere from Eastern Luzon to Taiwan and to Okinawa. These areas must continue monitoring the storm. We'll have another update tomorrow.
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Issued (0930 UTC) 530am PhT 061212
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