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Hurricane Barbara Discussion Number 8

Wiki-Hurricanes Forecast Center

2:00 PM PDT Mon Jul 1 2019

Barbara is now a hurricane. Conventional satellite imagery shows a well-organized cyclone, with a large and deep central dense overcast, a prominent spiral band in the southern semicircle, and expansive upper-level outflow in all directions. There have been no high-resolution microwave images since around the time of the previous advisory, but the most recent one did show the formation of an inner core, albeit one that was somewhat ragged at the time. The 18z satellite intensity estimate from TAFB is not available as of the time of this writing, but SAB awarded a T4.0/65kt. UW-CIMSS ADT has run higher, at T4.5/77kt. While a simple blend of these two values would support an initial intensity of 70kt, the most recent visible satellite frames give some cues that an eye may attempt to clear in the near term. Therefore, I have elected to set the initial intensity at the ADT value of 75kt.

Now that an inner core has formed, the chances of a period of rapid intensification are high. Wind shear, though not zero, has sufficiently relaxed to allow organization. Vortex-averaged Skew-Ts from the GFS indicate that mid-level relative humidity values are expected to remain above 80 percent over the next 4 days. Meanwhile, the SHIPS text file indicates ocean temperatures above 27C for the next 3 days. The culmination of these factors should allow for significant development in the short term; in fact, the SHIPS indicates a 7-in-10 chance that Barbara intensifies 25kt over the next 24 hours. The biggest question surrounding the intensity forecast is the large radius of maximum winds associated with Barbara, and whether this large size will make the hurricane susceptible to dry air intrusions that lower its ultimate peak. The 12z ECMWF posted its most intense run yet, bottoming Barbara out at 948mb. The SHIPS is the strongest solution, with a peak of 124kt, while the LGEM posts a Category 4 at 116kt. Both the HWRF and GFS are slightly less bullish, with minimum pressures around 959mb. A blend of these numbers supports upping the forecast peak strength to 115kt Category 4 intensity, although I have gone a little higher given the storm's quick development this morning relative to expectations. It would not be surprising Barbara fell a little on either side of this value. The environment after day 3 is expected to become rapidly hostile for the cyclone, with wind shear exceeding 20kt and ocean temperatures falling below 26C. Thus, the day 4 and 5 numbers have been sharply decreased again.

Barbara has been moving north of due west today, slightly south of model projections. A general west-northwest motion is expected to occur over the next 48 hours as mid-level ridging remains stout over northern Mexico. On days 3 and 4, a curve more toward the northwest seems in order as Barbara reaches the southwest periphery of the ridge. On day 5, though, the area of high pressure is expected to extend westward and force Barbara in that direction. The ECMWF has been north of most guidance for most of Barbara's lifespan, and this appears tied to the model's poor handling of the storm size. Now that the ECMWF has fallen in line with other guidance surrounding its large radius of maximum winds, the model has too come into consensus regarding Barbara's track, further increasing what was already a clear forecast.

FORECAST MAX WINDS

INIT 01/2100Z 75 KT 85 MPH

12H 02/0600Z 85 KT 100 MPH

24H 02/1800Z 100 KT 115 MPH

36H 03/0600Z 110 KT 125 MPH

48H 03/1800Z 120 KT 140 MPH

72H 04/1800Z 105 KT 120 MPH

96H 05/1800Z 70 KT 80 MPH

120H 06/1800Z 50 KT 60 MPH

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