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Typhoon Phanfone has pushed past the Mariana Islands and is poised to become a powerful typhoon in the days ahead, posing a threat to Japan this weekend.

Phanfone pushed through the northern Mariana Islands north of Guam Tuesday night as a tropical storm. High surf advisories continue for Guam, Rota, Tinian and Saipan through Friday night, where 7 to 9 foot surf is expected, particularly on west and south-facing reefs.

Typhoon Phanfone is now in a favorable environment of low wind shear and high sea-surface temperatures as it continues to track toward the northwest.

This should allow it to strengthen into a powerful typhoon later this week. A cycle of rapid intensification could occur, given the favorable environmental conditions. As a result, the U.S. military's Joint Typhoon Warning Center forecasts Phanfone to become the equivalent of a Category 4 tropical cyclone on the Saffir-Simpson Hurricane Wind Scale later this week.

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With the potential for Phanfone to become a very powerful tropical cyclone, the forecast track becomes critical.

Official forecasts from JTWC, as well as the Japan Meteorological Agency, show Phanfone gently curving northwestward and northward late this week into the weekend. This would take it past Iwo Jima and into a region of ocean west of Japan's Izu Islands and east of Japan's Ryukyu Islands, the two main north-south chains of small islands south of the Japanese mainland.

However, there are some key questions and uncertainties about Phanfone's track.

A bubble of high pressure sitting to the northeast of Phanfone will keep the cyclone on its west-northwestward to northwestward course over the next couple of days. Eventually, however, Phanfone should reach the western edge of that bubble -- and tropical cyclones often turn northward in those situations before eventually being forced northeastward by the prevailing upper-level westerlies, usually becoming post-tropical systems in the process.

However, if this bubble of high pressure stays relatively strong and the influence of the upper-level westerlies arrives later, Phanfone may not curve north and northeast as quickly. The major computer forecast models are not in good agreement on this issue, which becomes a critical question roughly 3 to 5 days from now.

As a result, there are several plausible scenarios:

- Phanfone curves sharply, passing south and east of mainland Japan and brushing the country with high waves and possibly a little bit of rain.

- Phanfone curves north a bit later, too late to miss Japan, and instead slams into the heavily populated Japanese mainland, anywhere from Tokyo in the east westward to Nagoya, Osaka, or Kobe in central Japan, or even Fukuoka in the west.

- Phanfone waits much longer to recurve, taking it more toward Okinawa, before recurving over much of mainland Japan.

Peak impacts would arrive in these areas Saturday through Monday, local time, if the second or third scenario above comes to pass.