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Tropical Depression Norbert Forecast Discussion Number 25

2020-10-15 04:37:52| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Wed Oct 14 2020 000 WTPZ44 KNHC 150237 TCDEP4 Tropical Depression Norbert Discussion Number 25 NWS National Hurricane Center Miami FL EP192020 800 PM PDT Wed Oct 14 2020 There are a few convective cells located more than 60 n mi to the west-northwest of Norbert's center, but for the most part, organized deep convection ceased around the time of the previous advisory. Assuming a spin down of the circulation since the afternoon ASCAT pass, and based on lower satellite estimates, Norbert's estimated intensity is now 25 kt. Further weakening is expected due to cool waters and moderate-to-strong shear, and if deep convection does not return soon, Norbert will degenerate into a remnant low overnight. Global model fields indicate that the remnant low will open up into a trough and dissipate just off the west coast of the Baja California peninsula in about 24 hours. Norbert has slowed down a bit, now that its shallower circulation is not being influenced by the steering around a mid-level low to its southwest as much as it was earlier today. The current motion is toward the north-northwest (330/12 kt), and Norbert is expected to slow down further until the time it dissipates. The updated NHC track forecast lies on top of the TVCE and HCCA consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 15/0300Z 25.7N 115.7W 25 KT 30 MPH 12H 15/1200Z 26.7N 116.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 24H 16/0000Z...DISSIPATED $$ Forecaster Berg

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Tropical Depression Norbert Forecast Discussion Number 24

2020-10-14 22:33:23| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Wed Oct 14 2020 000 WTPZ44 KNHC 142033 TCDEP4 Tropical Depression Norbert Discussion Number 24 NWS National Hurricane Center Miami FL EP192020 300 PM MDT Wed Oct 14 2020 Vertical wind shear and dry mid-level air are clearly taking a toll on Norbert. Infrared cloud top temperatures have rapidly warmed as Norbert has lost most, if not all, of its deep convection. Water vapor imagery shows a tongue of dry air drawn into the cyclone's circulation by a mid-level low pressure system centered to the west of Norbert. If current trends continue, Norbert could degenerate into a remnant low tonight or early Thursday. The advisory intensity is lowered to 30 kt based on a 1750Z ASCAT-B overpass that showed 25-30 kt winds in the northern semicircle of Norbert. This is consistent with T2.0 subjective Dvorak classifications from SAB and TAFB. Norbert has moved a bit faster than was previously forecast, and its initial motion is estimated at 330/15 kt. The track guidance consensus depicts a northwestward motion with a decrease in forward speed through tonight as the depression moves between a mid-level ridge over northern Mexico and the aforementioned mid-level low. A slow northward turn is expected on Thursday. The NHC track forecast was adjusted slightly to the right of the previous forecast based on 12Z global model trends. Norbert will continue weakening during the next day or so in an environment characterized by 20-25 kt of deep-layer shear, dry mid-level air, and low oceanic heat content. The official intensity forecast shows remnant low status at 24 h and dissipation at 36 h, which is consistent with the consensus of reliable global models. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 24.7N 114.9W 30 KT 35 MPH 12H 15/0600Z 25.9N 115.7W 25 KT 30 MPH 24H 15/1800Z 26.9N 115.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 16/0600Z...DISSIPATED $$ Forecaster Reinhart/Beven

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Tropical Storm Norbert Forecast Discussion Number 23

2020-10-14 16:46:13| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Wed Oct 14 2020 000 WTPZ44 KNHC 141446 TCDEP4 Tropical Storm Norbert Discussion Number 23 NWS National Hurricane Center Miami FL EP192020 900 AM MDT Wed Oct 14 2020 Recent satellite imagery suggests Norbert is beginning to feel the effects of deep-layer shear and drier mid-level air associated with a mid- to upper-level low pressure system centered to its west-northwest. While Norbert still shows signs of organization, the deepest convection is now displaced to the north of the estimated center position. The advisory intensity is held at 35 kt this morning based on objective and subjective current intensity Dvorak estimates from UW-CIMSS, SAB, and TAFB. It is likely that Norbert has peaked in terms of its intensity. Norbert's estimated initial motion is 325/13 kt. The cyclone is moving northwestward between a mid-level ridge over northern Mexico and the aforementioned mid- to upper-level low. This motion is expected to continue for the next 24 h, with a gradual decrease in forward speed as the upper low pulls away from Norbert. There is increasing spread noted in the model track guidance as the steering flow weakens between 24-48 h, but the general trend is for a slightly more northward motion during this time. Only minor adjustments were made to the official NHC track forecast, which remains close to the various consensus aids including TVCE and HCCA. Increasing deep-layer shear, drier mid-level air, and cooler sea-surface temperatures are expected to induce a weakening trend beginning later today, and Norbert will likely become a tropical depression this afternoon. The GFS simulated satellite imagery suggests Norbert will lose its deep convection within the next 24-36 h, and the official NHC forecast shows the system degenerating to a remnant low before dissipation at 48 h. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 23.1N 114.0W 35 KT 40 MPH 12H 15/0000Z 24.4N 115.0W 30 KT 35 MPH 24H 15/1200Z 25.6N 115.7W 25 KT 30 MPH 36H 16/0000Z 26.6N 115.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 16/1200Z...DISSIPATED $$ Forecaster Reinhart/Beven

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Tropical Storm Norbert Forecast Discussion Number 22

2020-10-14 10:37:08| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Wed Oct 14 2020 000 WTPZ44 KNHC 140837 TCDEP4 Tropical Storm Norbert Discussion Number 22 NWS National Hurricane Center Miami FL EP192020 300 AM MDT Wed Oct 14 2020 Norbert continues to produce a concentrated area of deep convection, but it has been very difficult pinpointing the exact location of the center overnight. Earlier ASCAT data and an 0152 UTC SSMIS microwave overpass suggests that the center could be a little north of the previous estimates, but overnight shortwave infrared imagery and TAFB and SAB fixes still place it closer to the southern portion of the convective mass. The advisory position is a compromise between the various estimates, but leans toward the previous track out of respect for continuity. Dvorak estimates from TAFB and SAB support an intensity of 35 kt, which is used as the initial wind speed for this advisory. The earlier ASCAT overpass revealed some slightly stronger wind vectors, but these appear to have been rain inflated. The initial motion estimate is a somewhat uncertain 325/13 kt. Norbert is moving northwestward between a mid-level ridge over northern Mexico and a mid- to upper-level low to its northwest. This general heading should continue over the next 24 to 36 hours with some reduction in forward speed as Norbert begins to weaken and is steered by the weaker low-level flow. The dynamical models are in general agreement, but there are differences in how fast and far north Norbert will move. The models that maintain a deeper cyclone depict a more poleward motion. The NHC track leans toward the southern solutions by 24 hours since Norbert is likely to weaken and become a more vertically shallow system by that time. Norbert only has a short window of opportunity in which to strengthen this morning. After that time, increasing southwesterly shear and cooler sea surface temperatures should begin to weaken the tropical storm. Norbert is likely to become a remnant low in 24 to 36 hours as it encounters sea surface temperatures below 26C, moderate to strong shear, and a more stable atmosphere. The global models indicate that the low will dissipate within a couple of days, and the NHC forecast follows suit. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 22.1N 113.3W 35 KT 40 MPH 12H 14/1800Z 23.5N 114.3W 35 KT 40 MPH 24H 15/0600Z 24.9N 115.2W 30 KT 35 MPH 36H 15/1800Z 26.0N 115.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 16/0600Z...DISSIPATED $$ Forecaster Brown

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Tropical Storm Norbert Forecast Discussion Number 21

2020-10-14 04:37:08| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Tue Oct 13 2020 000 WTPZ44 KNHC 140236 TCDEP4 Tropical Storm Norbert Discussion Number 21 NWS National Hurricane Center Miami FL EP192020 900 PM MDT Tue Oct 13 2020 Norbert has increased in organization this evening, with a pair of microwave passes as well as infrared satellite imagery showing a tightly curved band of convection wrapping about halfway around the low-level center. In addition, a well-defined outflow pattern is surrounding the cyclone in the current low-shear environment. Based on these developmental trends, the initial intensity has been increased to 35 kt, which is in agreement with the latest Dvorak intensity estimate from TAFB. There is only about a 12-18 h opportunity for Norbert to maintain its current strength or perhaps intensify a little more before it reaches a hostile environment just to its north. By 24 h, the cyclone is forecast to encounter strong southwesterly shear and a dry and stable atmospheric environment, while moving over cooler waters. Therefore, the cyclone should start weakening by 24 h and should degenerate into a remnant low devoid of deep convection by 48 h. The model guidance indicates the remnant low should dissipate very soon thereafter. The latest NHC intensity forecast is close to the latest consensus intensity guidance, and is only higher than the previous NHC forecast due to the increase in the initial intensity. Norbert has been moving northwestward at around 13 kt since this afternoon as the cyclone has been steered between a deep-layer ridge centered over northern Mexico and an upper-level low offshore of Baja California. As the upper low shifts westward over the next day or so, Norbert's forward speed should decrease. What remains of Norbert should then turn northward on Thursday within the low-level flow. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 21.0N 112.7W 35 KT 40 MPH 12H 14/1200Z 22.4N 113.8W 35 KT 40 MPH 24H 15/0000Z 24.2N 115.0W 30 KT 35 MPH 36H 15/1200Z 25.5N 115.6W 25 KT 30 MPH 48H 16/0000Z 26.5N 115.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 16/1200Z...DISSIPATED $$ Forecaster Latto

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