Parts of the U.S. Government are closed. However, because the information this site provides is necessary to protect life and property, it will be updated and maintained during the Federal Government shutdown. For critical weather information, please visit www.weather.gov. To learn more, see www.commerce.gov.
Tropical Storm ALETTA
ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM Tropical Storm Aletta Discussion Number 5 NWS National Hurricane Center Miami FL EP022018 900 PM MDT Wed Jun 06 2018 Deep convection has been bursting just to the northeast of the center during the past few hours, although a recent SSMI/S overpass suggests that the low-level circulation continues to consist of multiple swirls rotating around a common center. Because of the increase in convection, subjective satellite intensity estimates from TAFB and SAB have gone up to T3.0, so the initial intensity is set at 45 kt. There is about 15 kt of deep-layer southwesterly shear impinging on Aletta according to analyses from UW-CIMSS, which can be seen in the motions of the high cirrus emanating away from additional convection to the southwest. The global models aren't picking up on this shear very well, with the SHIPS diagnostics currently showing shear just under 10 kt. It now appears that some westerly shear could persist over Aletta for the next few days, and thus only modest intensification is expected over waters that are 27-29 degrees Celsius. The NHC official forecast still calls for Aletta to reach hurricane strength in a couple of days, and the updated forecast is close to the HCCA guidance and the intensity consensus through 48 hours. The intensity models are showing a faster weakening rate starting on day 3 due to cooler waters and higher shear, and although the NHC forecast has been trended downward to account for this, it still lies above much of the guidance later in the forecast period. The latest fixes indicate that Aletta is slowing down, and the initial motion estimate is 275/6 kt. A mid-level ridge centered over northwestern Mexico should continue to steer the cyclone slowly westward for a day or two. A continued slow motion to the west-northwest or northwest is then expected starting in 48 hours once Aletta reaches a break in the subtropical ridge. The ECMWF remains on the southern side of the guidance envelope, while the GFS, HMON, and HWRF lie on the northern edge. Since the upper-level patterns among these models are similar, the discrepancies among their respective tracks appear related to how strong they each make the cyclone, as the models with a stronger cyclone forecast a more northerly track. The new NHC forecast is closest to the HCCA guidance and is not too different from the previous official forecast. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 14.3N 108.4W 45 KT 50 MPH 12H 07/1200Z 14.5N 109.4W 50 KT 60 MPH 24H 08/0000Z 14.7N 110.4W 55 KT 65 MPH 36H 08/1200Z 14.9N 111.4W 60 KT 70 MPH 48H 09/0000Z 15.2N 112.3W 65 KT 75 MPH 72H 10/0000Z 16.3N 113.8W 75 KT 85 MPH 96H 11/0000Z 17.5N 115.5W 55 KT 65 MPH 120H 12/0000Z 18.0N 117.0W 35 KT 40 MPH $$ Forecaster Berg NNNN