Tropical Storm Flossie Winds: 40 kt
Pressure: 1003 mbar
Advisory 4 / 8:00 AM PDT Monday, July 29, 2019

Flossie has been faring better this morning on infrared imagery, putting out stout convection ahead of its rapidly moving self, but still has plenty of work to do in organizing itself internally. An unusually well-placed sequence of microwave data between about 4z and 12z suggested that the circulation was still quite elongated on a west-to-east axis with convection having some difficulty firmly rooting itself in the low-level cloud lines. There is some indication of improvement in the latest data, but not significantly so. SAB went with a current intensity of T3.0/45kt while UW-CIMSS ADT sits at T3.3/51kt. TAFB is lower at T2.5/35kt. A blend of these values suggests an intensity close to 45 kt, but the microwave data indicates this is likely inflated by disorganized convective noise, so I've only elected to raise the current intensity marginally to 40 kt.

Confidence is about as high as can be in the storm's track given the rather simple steering configuration and sound track guidance consensus through day 5. Westward motion is forecast for the next two days due to strong ridging over Baja California, with a slight west-northwest motion after that due to a transient upper-level low providing a weakness in the ridge.

For the next day or so, atmospheric conditions are exceptional, and if Flossie weren't moving so fast, it would probably be in the midst of rapidly intensifying right about now. Most parameters are favorable for the next three days. A trough in 2-3 days is expected to result in an increase in wind shear, generally in the 15-20kt range, though as discussed in prior advisories slight changes to the track and timing of both Flossie and the low may result in a favorable trough interaction. The shear itself is within marginally acceptable bounds such that Flossie may be able to at least somewhat withstand it. Afterwards, environmental parameters decline and suggest weakening on day 4-5, but the atmosphere is not abjectly inhospitable so we may see some longer-term persistence compared to its other fellow storms from the basin this season. I've entered more gradual intensification today in the forecast, but I would not be surprised to see some rapid intensification tonight given the emergence of a southwesterly dip in the high-resolution guidance. At 36-48 hours the divergent flow of the trough may aid in some rapid intensification right around then as well. Slow weakening is depicted late in the forecast, so it might be up to the Hawaiian shear wall to put an end to Flossie. Aside from an increase in some short-term values, the forecast generally looks the same as preceding advisories.


INIT 29/1500Z 40 KT 45 MPH

12H 30/0000Z 45 KT 50 MPH

24H 30/1200Z 55 KT 65 MPH

36H 31/0000Z 65 KT 75 MPH

48H 31/1200Z 80 KT 85 MPH

72H 01/1200Z 95 KT 110 MPH

96H 02/1200Z 90 KT 105 MPH

120H 03/1200Z 85 KT 100 MPH

Forecaster TheAustinMan
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