|Tropical Storm Erick||Winds: 35 kt|
|Pressure: 1005 mbar|
|Advisory 3 / 8:00 PM PDT Saturday, July 27, 2019|
Tropical Storm Erick has changed little in organization this evening. Visible satellite imagery indicates that a prominent spiral band has developed south of the circulation center, and that the spiral band to the north continues to persist. There has been little in the way of deep central convection today, though this has begun to change in recent frames. Satellite intensity estimates range from T2.0/30kt from both SAB and TAFB to T3.0/45kt from UW-CIMSS ADT. A blend of these values supports a possibly conservative 35kt as the initial intensity, in line with the ASCAT-C passes from several hours ago.
The track forecast is very straightforward, even by eastern Pacific standards. Broad mid-level ridging to the north of Erick should force the cyclone on a general west-northwest heading for the next 4 days, bringing it into the central Pacific about a day prior to that. By the end of the forecast period, the shallowness of the storm should yield a west to west-southwest motion. On this trajectory, Erick should pass south of the Hawaiian Islands, though this thinking is not set in stone yet.
The intensity forecast is more complicated. At face value, Erick is embedded within a favorable environment for strengthening, with wind shear expected to fall between 0-5 kt over the next 72 hours. Ocean temperatures are expected to be more than sufficient over that same period, only falling to marginal levels on day 4. Whether this becomes an issue for the cyclone will depend on its exact track. If Erick deviates south of forecast, warmer waters could allow the storm to maintain strength. If it moves north of forecast, a track over the 26C isotherm would prompt quicker weakening than forecast. Regardless of the track, the day 4 to 5 period will be characterized by an increase in upper-level winds; this shear will become downright hostile by the end of the period. Meanwhile, mid-level relative humidity values are forecast to remain adequate for three days or so, becoming increasingly unfavorable thereafter. There is a wide range in intensity solutions for Erick tonight. The GFS shows a storm knocking on the door of Category 2 strength, while the ECMWF struggles to make it a hurricane. The SHIPS and LGEM highlight a 70kt hurricane, which is a step up from their previous forecasts. The most bullish model is the notoriously reliable HWRF, which depicts Erick as a high-end Category 3 hurricane. The discrepancy in modelling may be at least partially attributable a strong convectively-suppressed kelvin wave traversing the East Pacific. This wave will attempt to suppress convection and may increase wind shear despite the favorable numbers indicated in the SHIPS file. Research in the effects of kelvin waves on tropical cyclone activity is still very much ongoing, and so the best course of action at this point is to reflect a forecast that incorporates the more aggressive SHIPS/LGEM models, while not going as far as the reliable HWRF. Obviously, this is a low confidence forecast. What appears less uncertain is that weakening will occur on days 4 and 5 as shear increases.
FORECAST MAX WINDS
INIT 28/0300Z 35 KT 40 MPH
12H 28/1200Z 40 KT 45 MPH
24H 29/0000Z 50 KT 60 MPH
36H 29/1200Z 60 KT 70 MPH
48H 30/0000Z 75 KT 85 MPH
72H 31/0000Z 85 KT 100 MPH
96H 01/0000Z 75 KT 85 MPH120H 02/0000Z 50 KT 60 MPH