ZCZC HFOTCDCP3 ALL TTAA00 PHFO DDHHMM TROPICAL STORM DARBY DISCUSSION NUMBER 44 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP052016 500 AM HST FRI JUL 22 2016 After decreasing through much of the night, deep convection around Darby has once again flared along the northern quadrant. Exposed low cloud bands across the southern semicircle show a reasonably well organized system, with good outflow to the northeast. Objective Dvorak satellite intensity estimates remain unchanged at 3.0/45 knots from all three analysis centers (HFO, JTWC and SAB). An 0718 UTC QSCAT pass showed a broad swath of 45 knot winds across the northern semicircle, with a small handful of 50 knot barbs thrown in. We will drop the initial intensity to 50 kt for this advisory based on this pass and eagerly await 53rd Weather Reconnaissance Squadron data, scheduled for arrival later this morning, to clarify Darby intensity. Initial motion is 270/10 kt, partially derived by rebesting the previous three best track points. While last evening's QSCAT pass depicted a center likely too far south, the overall impression from a growing body of microwave imagery was that Darby was actually several tenths of a degree south of where we though it was. Darby was relocated for this advisory. A 1223 UTC SSMI pass, received too late to use for this advisory, hints that Darby may need to be relocated westward later. Track guidance is tightly packed depicting a gently curving path along or just east of the Hawaiian Islands between 36 and 72 hours. The exception is GFDL, which wants to divert Darby almost due northward beyond 24 hours. Our forecast track fits in the envelope, closely following TVCN consensus. Adjustments were made to account for relocation. However, that portion of the track closest to the Hawaiian Islands changed very little. Darby continues to move along the southern flank of a ridge centered north of Hawaii and will continue to do so through 36 hours. Afterwards, a deep low will dig south and weaken the ridge, slowing this system down and allowing Darby to curve gently northwestward from 36 to 72 hours, then northward beyond 72 hours. Intensity guidance varies from SHIPS, which rapidly weakens Darby after 48 hours, to GHMI, which maintains current strength throughout. The effects of shear and slightly warmer SSTS are expected to essentially cancel each other out through 48 hours, with the weakening effects of shear becoming dominant afterwards as Darby gains latitude. Any weakening effects that land interaction would have on Darby intensity have been ignored so far. Our intensity forecast depicts Darby as weaker at all tau than previous advisories, with this system finally becoming a depression on day 5. Interests outside of the watch and warning areas in the Hawaiian islands should monitor the progress of Darby, as it could eventually have impacts on all islands through early next week. Remember, it is important not to focus too closely on the exact track and intensity forecasts because the average track error 72 hours out is near 100 miles, while the average intensity error is about 15 kt. In addition, the hazards of a tropical cyclone can extend over a broad area well away from the center. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 18.6N 149.2W 50 KT 60 MPH 12H 23/0000Z 18.7N 150.9W 45 KT 50 MPH 24H 23/1200Z 19.0N 152.8W 45 KT 50 MPH 36H 24/0000Z 19.7N 154.4W 45 KT 50 MPH 48H 24/1200Z 20.7N 155.7W 45 KT 50 MPH 72H 25/1200Z 23.0N 158.2W 40 KT 45 MPH 96H 26/1200Z 26.5N 160.5W 35 KT 40 MPH 120H 27/1200Z 31.3N 161.6W 30 KT 35 MPH $$ Forecaster Powell NNNN