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Tropical Depression Narda Forecast Discussion Number 6
2019-09-29 22:58:39| National Hurricane Center (East Pacific)
Issued at 400 PM CDT Sun Sep 29 2019 000 WTPZ41 KNHC 292058 TCDEP1 Tropical Depression Narda Discussion Number 6 NWS National Hurricane Center Miami FL EP162019 400 PM CDT Sun Sep 29 2019 Narda has become less organized during the past several hours. The primary center has been over the mountains of southwestern Mexico between Lazaro Cardenas and Manzanillo, and the associated convection has been decreasing. A 17Z ASCAT-C overpass suggests two other vorticity centers are located offshore, one near a cluster of convection to the southwest of Manzanillo and the other to the southwest of Lazaro Cardenas. The scatterometer data showed 35 kt winds southeast of the primary center, and given the decrease in organization since that time it is estimated that Narda has dropped below tropical storm strength. The initial motion is a rather uncertain 315/17 kt, which is faster than in the previous advisory. Over the next couple of days, Narda will be steered generally northwestward close to the coast of mainland Mexico along the southwestern periphery of a large high pressure area. After that time, a mid- to upper-level trough approaching the northern Baja California peninsula from the west should cause the system to turn north-northwestward and move over northwestern mainland Mexico. The track guidance has shifted to the right since the last advisory. However, due to the uncertainty in what will happen to the center, including the possibility it could re-form offshore, the new forecast track will be to the left of the model consensus. The new track will be faster than the previous track based on a combination of the initial motion and faster guidance. The intensity forecast is highly uncertain. The official forecast will follow the previous forecast in calling for Narda to weaken while over Mexico, and then re-intensify a little when the system emerges over water. However, there remain two alternative scenarios. The first of these is that the circulation dissipates completely as it passes over the mountains of western Mexico. The second is that the center re-forms offshore, either from the vorticity center currently southwest of Manzanillo or, as suggested by some of the global models, from a new center north of Cabo Corrientes. If such a re-formation occurs, this could lead to significant changes in both the intensity and the track forecasts. The primary threat from Narda is very heavy rainfall, which should result in life-threatening flash flooding and mudslides over portions of the southern coast of Mexico. Rainfall totals of up to 15 inches are possible. This rainfall threat is expected to continue even if the system dissipates as a tropical cyclone. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 19.1N 103.5W 30 KT 35 MPH...INLAND 12H 30/0600Z 20.8N 105.2W 25 KT 30 MPH...INLAND 24H 30/1800Z 23.0N 106.9W 25 KT 30 MPH...OVER WATER 36H 01/0600Z 24.7N 108.4W 30 KT 35 MPH 48H 01/1800Z 25.7N 109.5W 35 KT 40 MPH 72H 02/1800Z 28.5N 110.5W 30 KT 35 MPH...INLAND 96H 03/1800Z...DISSIPATED $$ Forecaster Beven
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