000 WTPZ42 KNHC 102033 TCDEP2 Tropical Storm Aletta Discussion Number 21 NWS National Hurricane Center Miami FL EP022018 200 PM PDT Sun Jun 10 2018 Despite southerly vertical wind shear of about 15 kt, Aletta has been able to maintain a small cluster of strong convection in the northwestern quadrant. Recent ASCAT passes missed the now partially exposed low-level center and much of the inner-core wind field, but they did manage to capture tropical-storm-force winds in the eastern semicircle. Also, a Mexican Navy automated weather station on Clarion Island reported a sustained wind of 33 kt and a gust to 47 kt a few hours ago as an outer band passed over the island. Based on that observation, along with a TAFB Dvorak estimate of T3.0/45 kt, the intensity is being maintained at 40 kt for this advisory. Microwave satellite position fixes indicate a motion of about 280/06 kt since the previous advisory. No significant changes to the previous forecast track were required. The new model guidance remains in fair agreement on Aletta moving slowly westward for the next 48-72 h along the southern periphery of a weak low- to mid-level ridge to the north of the cyclone. After that time, steering currents are forecast to collapse, along with Aletta coming under the influence of rapidly strengthening Hurricane Bud currently located to the east-southeast, which could result in the shallow cyclone stalling. The official forecast track is similar to the previous advisory and remains in the middle of the tightly packed track model guidance. Although the wind shear is forecast to weaken to less than 10 kt during the next 24-36 hours, which would generally favor re-strengthening, Aletta will also be moving over sub-26C SSTs and into a drier and more stable airmass. The poor thermodynamics, along with cold-air stratocumulus clouds already being ingested into the western and southern quadrants of the cyclone, argues for gradual weakening to occur over the next day or so, with Aletta degenerating into a remnant low pressure system by Tuesday. A steady spin down of the low is expected during the 72-120 hour period, with the shallow cyclone possibly even dissipating on day 5. The official intensity forecast is similar to the previous advisory, and closely follows a blend of the HCCA and IVCN consensus intensity models. FORECAST POSITIONS AND MAX WINDS INIT 10/2100Z 16.6N 115.7W 40 KT 45 MPH 12H 11/0600Z 16.6N 116.6W 35 KT 40 MPH 24H 11/1800Z 16.6N 117.6W 30 KT 35 MPH 36H 12/0600Z 16.5N 118.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 12/1800Z 16.4N 119.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 13/1800Z 16.2N 120.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 14/1800Z 16.1N 120.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 15/1800Z 15.9N 121.1W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart