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Tropical Depression Sixteen-E Forecast Discussion Number 1
2020-09-13 04:38:29| National Hurricane Center (East Pacific)
Issued at 900 PM MDT Sat Sep 12 2020 000 WTPZ41 KNHC 130238 TCDEP1 Tropical Depression Sixteen-E Discussion Number 1 NWS National Hurricane Center Miami FL EP162020 900 PM MDT Sat Sep 12 2020 The last few visible satellite images indicated convection growing closer to the center of a low pressure area that NHC has been tracking for the past few days. Since the low was already well-defined this afternoon, the development of organized deep convection means that a tropical depression has formed. The initial wind speed is set to 30 kt, which is a blend of the TAFB/SAB fixes and earlier ASCAT data. The depression is embedded within a moderate easterly wind-shear environment, partially related to its position in the larger ITCZ/monsoon trough structure. Global model guidance is in reasonable agreement on the large-scale circulation becoming focused on the new tropical cyclone and a slight relaxation of the shear during the next couple of days. This change should lead to gradual intensification, and the new forecast is between the model consensus and the corrected-consensus aids. Beyond 2-3 days, decreasing SSTs and increasing dry air entrainment should promote weakening, and that is reflected below. The initial motion estimate is an uncertain northwestward or 315/08 kt. A mid-level ridge is forecast to build westward, causing the cyclone to move west-northwestward for a few days after the weekend. A westward turn is forecast at long range due to the shallow cyclone feeling the low-level ridge. One big uncertainty with this forecast is how it interacts with the larger ITCZ/monsoon trough circulation, including the remnants of Invest 91E. For now, it is assumed that only a slight slow down occurs as the depression becomes the dominant circulation in the area, and the forecast is more consistent with the GFS- or UKMET-based guidance. However, a slower ECMWF-like solution is also possible, but is being given less weight at this time. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 16.7N 112.9W 30 KT 35 MPH 12H 13/1200Z 17.5N 113.8W 35 KT 40 MPH 24H 14/0000Z 18.3N 115.4W 40 KT 45 MPH 36H 14/1200Z 18.9N 116.9W 45 KT 50 MPH 48H 15/0000Z 19.5N 118.5W 50 KT 60 MPH 60H 15/1200Z 20.0N 119.9W 55 KT 65 MPH 72H 16/0000Z 20.5N 121.0W 55 KT 65 MPH 96H 17/0000Z 21.5N 123.5W 45 KT 50 MPH 120H 18/0000Z 21.5N 126.0W 30 KT 35 MPH $$ Forecaster Blake
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