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Typhoon Mirinae was born from the developing Tropical Storm 23W, as expected. The storm has been moving along at a pretty good clip. So far it has tended to move faster than the general forecast. I suspect that is why the Joint Typhoon Warning Center has gone along with the early forecast landing in the Philippines at around 12Z October 30 that is brought out by the NOGAPS model. The GFS is remarkably similar to the NOGAPS in the track and intensity with both advertising a tropical cyclone with a central pressure somewhere between 992 and 1000 mb near the same location in the Luzon province that Typhoon Parma struck. But, the GFS wants to take the storm into the Philippines somewhere between 12z and 18z October 31. Given the persistent forward speed and little evidence that there is much out there to slow this guy down, the early forecast landfall is probably a fair bet.

Tropical Storm 23W not only has been moving faster than forecast, it also has developed faster than forecast. It was not anticipated by the JTWC to become Typhoon Mirinae until 12Z October 28 but had done so by 18Z October 27. That is not overly significant except that it is obviously in a upswing mode. The risk here is that with the storm’s forward speed and the fact that its in an intensication process, odds are pretty high that the Philippines will be struck by a tropical cyclone that is intensifying, not weakening. One thing that has been right on the money is the forecast track. Typhoon Mirinae moved northwest south of Saipan near Andersen Air Force base while it was still Tropical Storm 23W. As anticipated, the storm went a few hundred more miles on that course and now has taken a more westerly track. The good news is that the forward speed that it is showing and that is forecast will mean that it would cross the Philippines in less than 24 hours. That would tend to cut down on excessive rain, though very heavy rain in a short period of time can be expected.

The bad news is that Luzon cannot handle much in the way of heavy rain. The storm flow will be slamming into the same mountainous regions that experienced mudslides from Typhoon Parma and Tropical Storm Ketsana and those mountains will do nothing but enhance the rainfall rates. If the forecast holds and verifies, then Typhoon Mirinae will hit in almost the exact same spot at Typhoon Parma and will track due west near Manila, similar to Tropical Storm Ketsana. Also, the forward momentum and expected maximum winds of 100 kts would create a pretty good storm surge to the right of the center of the landfall, which is something that did not occur with either Typhoon Parma or Tropical Storm Ketsana. The flood ravaged Philippines is no where close to recovering from Parma and Ketsana as disease has now broken out in Luzon. The World Health Organization is helping to try and control an outbreak of leptospirosis and if Mirinae does as expected, the situation will do nothing but get worse.

There is one more bit of bad news that could prove to be the biggest factor in the saga of the Philippines. When I looked beyond the landfall time of Typhoon Mirinae, I noticed that the typhoon moves across the South China Sea into Vietnam, which means the exact same areas that got hit by Ketsana in both the Philippines and Vietnam will get nailed again and some of the areas affected in Vietnam by Parma will also get heavy rains and wind from Mirinae. But, maybe more importantly I noticed another tropical cyclone right on the heels of Typhoon Mirinae. It is not that well developed at only about 1008 mb. But, both the NOGAPS and the GFS show this feature and it is forecast to track right into Luzon. Often, a weak tropical cyclone can bring extremely heavy rains. Since they are not well developed, they don’t necessarily follow typical steering trends and often times will slow down and fall apart over one area, dropping a lot of rain. This scenario is many days away if it were to occur, but it is showing up on at least two models. So, its’ worth noting.

WDPN32 PGTW 280300 MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (MIRINAE) WARNING NR 09// RMKS/ 1. FOR METEOROLOGISTS. 2. 12 HOUR SUMMARY AND ANALYSIS. A. TYPHOON (TY) 23W (MIRINAE) IS TRACKING WESTWARD OVER THE PAST 12 HOURS AND HAS RAPIDLY INTENSIFIED TO 75 KNOTS. DVORAK ESTIMATES FROM PGTW, KNES AND RJTD CURRENTLY SUPPORT INTENSITIES FROM 75 TO 90 KNOTS. THIS FORECAST IS PRIMARILY BASED ON THE PGTW AND RJTD ESTIMATES. MICROWAVE IMAGERY OVER THE PAST 12 HOURS HAS SHOWN A WELL DEFINED EYE HAS DEVELOPED, AND IS BEGINNING TO BE APPARENT IN MULTISPECTRAL IMAGERY AS WELL. THE POLEWARD OUTFLOW CHANNEL HAS REMAINED WELL ESTABLISHED OVER THE PAST 12 HOURS WITH THE MID- LATITUDE TROUGH NORTH OF TY 23W THAT HAS STARTED TO LIFT OUT TO THE NORTHEAST. STRONG ZONAL FLOW ACROSS SOUTHERN JAPAN IN THE UPPER LEVEL HAS STARTED TO REPLACE THE TROUGH AS THE PRIMARY MECHANISM FOR POLEWARD OUTFLOW. THE COMBINATION OF THE TROUGH AND DEVELOPING ZONAL FLOW HAS SUPPORTED THE RECENT INTENSITY CHANGE OBSERVED. RADIAL OUTFLOW, ASSOCIATED WITH AN UPPER LEVEL POINT SOURCE ANTI-CYCLONE LOCATED TO THE EAST OF TY 23W, HAS MAINTAINED AN EQUATORWARD OUTFLOW CHANNEL OVER THE PAST 12 HOURS. 3. FORECAST REASONING A. THE FORECAST REASONING HAS NOT CHANGED SINCE THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. TY 23W WILL MAINTAIN A GENERAL WESTWARD TRACK TOWARDS LUZON THROUGH TAU 72 UNDER THE INFLUENCE OF A WELL ESTABLISHED MID-LEVEL SUBTROPICAL RIDGE (STR) LOCATED TO THE NORTH OF MIRINAE. OUTFLOW FROM THE MID-LATITUDE TROUGH AND ZONAL FLOW WILL DIMINISH SLIGHTLY OVER THE NEXT 24 HOURS, BUT CONTINUED RADIAL OUTFLOW WILL ALLOW FOR STEADY INTENSIFICATION THROUGH TAU 72. THE INTENSIFICATION WILL BE SUPPORTED BY LOW VERTICAL WIND SHEAR CONDITIONS PERSISTING THROUGH THE ENTIRE FORECAST, ALONG WITH FAVORABLE SEA SURFACE TEMPERATURES AND OCEAN HEAT CONTENT. C. BEYOND TAU 72 MIRINAE IS EXPECTED TO MAKE LANDFALL WITH LUZON, WEAKEN AND SLOW SLIGHTLY DUE TO THE LAND INTERACTION, THEN CROSS INTO THE SOUTH CHINA SEA AROUND TAU 96. AS THE SYSTEM RE- CONSOLIDATES THE INTENSITY IS EXPECTED TO REMAIN STEADY THROUGH TAU 120. MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THE FOLLOWING FORECAST, EXCEPT WITH THE SPEED OF ADVANCE OVER LUZON. MODELS SUGGEST LITTLE TO NO SLOW-DOWN AS TY 23W CROSSES OVER LUZON. THE FORECAST INCORPORATES A DECREASE IN TRACK SPEED FROM TAU 72 THROUGH 120 BASED ON LAND INTERACTION WITH THE LOW LEVEL CIRCULATION.// NNNN