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 680 
 WTPZ45 KNHC 290233
 TCDEP5
 
 Tropical Storm Miriam Discussion Number  12
 NWS National Hurricane Center Miami FL       EP152018
 800 PM PDT Tue Aug 28 2018
 
 There's been little change in the overall cloud pattern of Miriam
 during the past several hours.  An earlier Advanced Technology
 Microwave Sounder (ATMS) overpass and a 2053 UTC GCOM-W1 AMSR2 image
 indicate that the surface center is still sheared to the northwest
 of the deep convective banding feature encompassing the southern
 portion of the cyclone.  Dvorak satellite intensity estimates from
 TAFB and SAB remain unchanged, and a 2213 UTC SATCON analysis
 showed 51 kt.  Based on these data, the initial intensity is held
 at 50 kt.
 
 The intensity forecast is rather problematic this evening.
 Decay SHIPS guidance (both GFS and ECMWF background fields) shows
 the moderate northwesterly shear increasing after 48 hours, while
 indicating little change in strength up to that period.  After that
 time, these statistical/dynamical guidance models quickly degenerate
 the cyclone into a remnant low in 4 days.  The NOAA-HCCA, HWRF, and
 the IVCN consensus model, on the other hand, all show Miriam
 becoming a hurricane in 36-48 hours.  For this advisory, I've
 elected to maintain continuity and show gradual strengthening to
 just below hurricane strength in 36 hours, with a weakening trend
 commencing in 3 days.  All the deterministic models agree with
 Miriam becoming a remnant low in 5 days, and this is reflected in
 the NHC forecast.
 
 The initial motion is estimated to be westward, or 270/11 kt,
 within the easterly mid-level steering flow produced by a
 mid-tropospheric high to the north of Miriam.  The cyclone is
 expected to turn toward the northwest in 36 hours, then
 rather abruptly north-northwestward in 2 days and continuing on
 through day 4, in response to a large mid- to upper level cutoff low
 digging southwestward toward the Hawaiian Islands.  A large spread
 in the models still exists in the latter portion of the forecast, as
 mentioned in the previous advisory.  The track forecast philosophy
 remains unchanged with a nudge more toward a blend of the TVCN
 consensus and the global models that show a gradual turn back toward
 the northwest due to a shallower vertical structure near the end of
 the period.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  29/0300Z 14.1N 137.4W   50 KT  60 MPH
  12H  29/1200Z 14.2N 138.9W   50 KT  60 MPH
  24H  30/0000Z 14.5N 140.4W   55 KT  65 MPH
  36H  30/1200Z 15.4N 141.4W   60 KT  70 MPH
  48H  31/0000Z 16.7N 141.8W   60 KT  70 MPH
  72H  01/0000Z 20.2N 142.0W   55 KT  65 MPH
  96H  02/0000Z 23.4N 143.6W   40 KT  45 MPH
 120H  03/0000Z 26.5N 146.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
 $$
 Forecaster Roberts
 
 
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