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The Typhoon Mirinae Forecast Track remains generally unchanged as does the intensity. It continues to move west at a pretty good clip and that may end up being a good thing for the Philippines. The JTWC forecast track has been nudged a tad farther south than previous runs which would send the typhoon across the island closer to Manila. While Luzon really can’t handle a lot of rain, it’s going to get it as well as winds along the coast perhaps as high as 105 to 110 mph or 95 kts with higher gusts. With the forward momentum of Mirinae, I suspect that whatever the maximum storm surge in that area with this type of storm will be likely. The biggest difference between the NOGAPS and GFS models is the timing. Over 117,000 Filipinos remain in shelters as a result of Typhoon Parma and Tropical Storm Ketsana. So, the government of the Philippines is warning the potential for landslides and flooding. The government is particularly concerned because All Saints Day, November 1, is traditionally a day when Filipinos visit cemeteries to remember ancestors.
The NOGAPS advertises a typhoon moving at a pretty good pace with a landfall outlined just prior to 12Z on Friday October 30. It also favors a landfalling tropical cyclone with a central pressure a shade less than 996 mb. The GFS on the other hand doesn’t come up with as robust a system as the NOGAPS. The central pressure at landfall is something between 996 mb and 100 mb. If that is verified, I find it hard to determine how a storm with that level of pressure could support the JTWC contention that a 95 kt typhoon will strike the Philippines. My experience tells me that pressures that high generally does not support winds of 95 kts unless it was a major tropical cyclone that was winding down and even that is not evidence of support. Falling winds mean that the pressure cannot support that wind level. Other than that, the GFS is much slower than the NOGAPS with a landfall with a landfall not coming until just after 00Z on Saturday Oct 31. That is a big difference because if Mirinae moves that slowly then it would be dropping heavy rain on the Philippines for many hours longer than the NOGAPS solution.
The typhoon has been moving at a steady speed and so unless something shows up to slow its forward speed then it seems reasonable that the JTWC forecast of having the core of the storm over Luzon for less than 24 hours is very plausible. On the other hand, that also means that the fine folks of Manila and other parts of the Philippines will probably experience pretty decent winds….maybe even typhoon force…for the duration of the storm because Mirinae just wouldn’t have time to fall apart…but it will weaken. This storm got stronger than anticipated due to a trof to the north that was enhancing the outflow to the north. Interestingly, that trof was actually created from the remnant of Typhoon Lupit which moved northeast offshore of Japan, turned extratropical and created a front trailing off from it. With that feature moving out, there isn’t any real mechanism that would help enhance the intensity substantially. The only thing that will help it get stronger is an increasing outflow aloft, but that will be offset somewhat by a little bit of vertical shear. The JTWC notes that the shear has already messed up the visibility of the eye.
If one assumes a rapid movement across the Philippines, then one might assume that the storm will not deteriorate that much over land and will emerge in the South China Sea in good shape. So good that it may redevelop. But, sea surface temperatures in the central South China Sea have dropped off a bit due to a recent shot of unseasonably cold air in the area. So, the JTWC forecast reflects that situation by reducing the intensity of the storm as it approaches Vietnam. Mirinae may fall to tropical storm status before landfall. However, Vietnam also suffered from Typhoon Ketsana and Typhoon Parma, though Parma was closer to Hanoi. In any event, the ground in Vietnam is pretty saturated so if they get a tropical storm instead of a typhoon, it is really immaterial as the forward motion will be the key for Vietnam. Vietnam suffered over 3/4 of a billion US dollars just from Ketsana. If the storm slows down once it’s inland over SE Asia, then excessive rainfall can be anticipated. The thing that everyone wants is for the storm to keep moving.
WDPN32 PGTW 290300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (MIRINAE) WARNING NR 13//
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
A. TYPHOON (TY) 23W (MIRINAE) HAS INTENSIFIED TO 90 KNOTS AND
MAINTAINED A WESTWARD TRACK UNDER THE INFLUENCE OF THE SUBTROPICAL
STEERING RIDGE OVER THE PAST 12 HOURS. RECENT ANIMATED MULTISPECTRAL
IMAGERY SHOWS EVIDENCE OF EASTERLY VERTICAL WIND SHEAR THAT HAS
CAUSED MIRINAE TO LOSE ITS EYE-LIKE FEATURE OVER THE LAST 12 HOURS.
HOWEVER, THE SYSTEM STILL HAS GOOD POLEWARD OUTFLOW INTO THE MID-
LATITUDE WESTERLIES AS WELL AS ACCESS TO POLEWARD OUTFLOW INTO THE
TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) LOCATED APPROXIMATELY 15
TO 20 DEGREES EAST OF THE SYSTEM. THE CURRENT POSITION IS BASED WITH
HIGH CONDIFENCE ON POSITION FIXES BY RJTD AND PGTW AND IS SUPPORTED
BY A 282127Z SSMI MICROWAVE IMAGE. THE CURRENT INTENSITY IS BASED ON
DVORAK ESTIMATES OF 90 KNOTS FROM PGTW AND RJTD.
3. FORECAST REASONING.
A. THE FORECAST REASONING HAS NOT CHANGED SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
B. THE TYPHOON WILL CONTINUE TO TRACK WESTWARD THROUGH THE
FORECAST PERIOD AND WILL RETAIN RADIAL OUTFLOW, ENABLING EXHAUST
INTO THE MID-LATITUDES, AS IT TRACKS SOUTH OF A NARROW SUBTROPICAL
RIDGE. FURTHER INTENSIFICATION IS EXPECTED TO BE LIMITED, MAINLY DUE
TO THE LACK OF A STRONG (POLEWARD) OUTFLOW CHANNEL AS THE SYSTEM
TRACKS FURTHER AWAY FROM THE TUTT MENTIONED IN PARA 2.A. MIRINAE IS
EXPECTED TO MAKE LANDFALL IN THE PHILIPPINES AND WEAKEN JUST BEFORE
C. BEFORE TAU 72 THE SYSTEM WILL EXIT LUZON INTO THE SOUTH CHINA SEA
AS A MUCH-WEAKENED TYPHOON. A COOLER POOL OF SEA SURFACE TEMP-
ERATURES IN THE CENTRAL SOUTH CHINA SEA, MINIMAL OCEAN HEAT CONTENT
VALUES AND DIMINISHED POLEWARD EXHAUST WILL PROMOTE STEADY
WEAKENING. AN EARLY SEASON COLD SURGE WILL ALSO AID IN WEAKENING THE
SYSTEM CLOSER TO TAU 96. THE MODEL GUIDANCE IS IN STRONG AGREEMENT
WITH THIS FORECAST SCENARIO. THEY ALSO SHOW A GROWING TREND TOWARDS
A MORE SOUTHWESTERN TRACK IN THE EXTENDED TAUS.//