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Hurricane Barbara Discussion Number 12

Wiki-Hurricanes Forecast Center

2:00 PM PDT Tue Jul 2 2019

Barbara has blossomed into a spectacular Category 4 hurricane today. The storm has been sporting a large eye that has warmed upwards of 20C outside of the influence of vortex rossby waves that have occasionally allowed eyewall debris into the center. It is embedded within a symmetrical and expansive central dense overcast, where convection cooler than -75C has wrapped halfway around the center. While 18z satellite intensity estimates from SAB and TAFB were T6.0/115kt, these values represent strict Dvorak interpretation based on a CDO that was in flux at the time of analysis. In these cases, UW-CIMSS ADT may do a better job of highlighting the totality of a storm's structure, and it currently assesses Barbara at T6.9/137kt. A blend of these values supports 120kt, but I have elected to place more weight on the latter value and assign 125kt.

While wind shear remains light and ocean temperatures remain warm, drier air is beginning to have an influence on Barbara. Two microwave passes from 14z and 18z showed that convective activity was beginning to diminish across the western semicircle, and that the northern eyewall was not as intense as surrounding quadrants as drier air tried -- largely unsuccessfully for now -- to wrap into the center. Mid-level relative humidity values are only going to continue decreasing, making the hurricane increasingly susceptible to structural disruption. That being said, the fact that Barbara has a large eye makes it less prone to eyewall replacement cycles, and so a significant decrease in strength does not appear particularly likely in the short term. The intensity forecast will blend both of these avenues and highlight a steady-state cyclone for the next 12 hours. A slow decline is forecast for the 24 and 36 hour points, with rapid weakening thereafter as Barbara encounters wind shear over 15kt (upwards of 40kt by day 5!) and ocean temperatures near 25C. Degeneration is now forecast on day 5 as Barbara crosses into the Central Pacific.

Barbara is now beginning to take on a more northwestward trajectory as the mid-level ridge over northern Mexico weakens and the hurricane reaches the southwestern periphery of the high. A general northwest track should continue for the next 3 days, but a curve toward the west or even west-southwest is expected on days 4 and 5 and the ridge restrengthens and Barbara becomes increasingly steered by low-level trade winds.

FORECAST MAX WINDS

INIT 02/2100Z 125 KT 145 MPH

12H 03/0600Z 125 KT 145 MPH

24H 03/1800Z 120 KT 140 MPH

36H 04/0600Z 105 KT 120 MPH

48H 04/1800Z 90 KT 105 MPH

72H 05/1800Z 55 KT 65 MPH

96H 06/1800Z 35 KT 40 MPH

120H 07/1800Z 25 KT 30 MPH...POST-TROP/REMNT LOW

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