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Tropical Storm Alvin Forecast Discussion Number 4

2019-06-26 16:53:48| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Wed Jun 26 2019 000 WTPZ41 KNHC 261453 TCDEP1 Tropical Storm Alvin Discussion Number 4 NWS National Hurricane Center Miami FL EP012019 900 AM MDT Wed Jun 26 2019 Visible and passive microwave imagery this morning indicate that the center of the tropical cyclone is located farther south than previously estimated, possibly due to a reformation of the center. The center of the cyclone is now embedded near the deepest inner- core convection, and some overall improvement in the convective pattern is evident. Satellite intensity estimates indicate that the cyclone has reached tropical storm strength, and the initial intensity of 35 kt is based on the latest Dvorak estimate from SAB. Alvin's formation marks the 3rd latest date of the development of the first named storm in the eastern Pacific basin during the satellite era (since 1966). Alvin has turned a little south of due west and the initial motion estimate is 260/12 kt. The new NHC forecast track over the first couple of days has been adjusted southward, in large part due to the more southerly reformation of the center. Despite this, the overall track forecast philosophy has not changed. Alvin is expected to move westward and then west-northwestward with a gradual decrease in forward speed over the next few days along the southwestern periphery of a subtropical ridge. There remains about a 24-36 hour window for some additional strengthening to occur over warm SSTs in a low-shear and sufficiently moist environment. This environment, combined with the improving structure of the storm, supports raising the intensity forecast a little in the near term. The new NHC forecast is in good agreement with the dynamical models and the intensity consensus. After 36 hours, the forecast track takes Alvin over progressively cooler waters and into a drier and higher-shear environment. This should result in steady weakening, with the cyclone likely becoming devoid of deep convection by 72 hours, and dissipating by day 5. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 14.7N 109.4W 35 KT 40 MPH 12H 27/0000Z 14.7N 111.4W 45 KT 50 MPH 24H 27/1200Z 15.0N 113.7W 45 KT 50 MPH 36H 28/0000Z 15.7N 115.8W 45 KT 50 MPH 48H 28/1200Z 16.4N 117.7W 40 KT 45 MPH 72H 29/1200Z 17.4N 121.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 30/1200Z 18.0N 124.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 01/1200Z...DISSIPATED $$ Forecaster Latto/Brennan

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Tropical Depression One-E Forecast Discussion Number 3

2019-06-26 10:34:19| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Wed Jun 26 2019 000 WTPZ41 KNHC 260834 TCDEP1 Tropical Depression One-E Discussion Number 3 NWS National Hurricane Center Miami FL EP012019 300 AM MDT Wed Jun 26 2019 The overall convective pattern of the cyclone has changed little since the previous advisory. However, passive microwave images indicate that the low-level center has become less distinct and that the inner-core convection has become ragged. In addition, the coldest cloud tops have migrated from north through east to now south of the center during the past 12 hours, another indication that the inner-core of the depression is undergoing some structural changes. Although no ASCAT wind data are available over the cyclone's core, a 0417Z ASCAT-C pass did catch the western portion of the circulation and only showed northerly winds of 5-10 kt within 30 nmi of the center, which suggests that the surface wind field might not be as well developed as the circulation aloft is. The initial position and the 275/13-kt motion are based on a blend of microwave and conventional fixes, and also continuity with the previous motion vector. The latest track model guidance is in decent agreement on a westward to west-northwestward motion accompanied by a gradual decrease in forward speed over the next few days as a strong deep-layer subtropical ridge holds steady to the north of the cyclone. The new NHC track forecast is similar to but south of the previous advisory track, mainly due to the more southerly initial position. As mentioned in the previous forecast package, the 00Z ECMWF model continues to show a more southward dip in the track during the next 24 h. That is a viable alternate track scenario if the center redevelops farther south closer to the coldest overshooting cloud tops later this morning. There is a narrow window of opportunity for the system to strengthen into a tropical storm during the next 24 h or so while the cyclone remains over warm water and in low vertical wind shear conditions. By 36-48 hours, the cyclone is expected to move over sub-26C SSTs and into a more stable environment that is not conducive for generating vigorous convection despite the favorable low-shear conditions forecast at that time. The combination of cooler waters, drier mid-level air, and increasing southwesterly wind shear shear are expected to induce steady weakening in 48-96 hours, with dissipation forecast by 120 h. The official intensity forecast is similar to the previous advisory, and follows the IVCN and ICON intensity consensus models. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 15.5N 108.3W 30 KT 35 MPH 12H 26/1800Z 15.6N 110.3W 35 KT 40 MPH 24H 27/0600Z 15.8N 112.7W 35 KT 40 MPH 36H 27/1800Z 16.4N 114.9W 35 KT 40 MPH 48H 28/0600Z 17.0N 116.9W 30 KT 35 MPH 72H 29/0600Z 18.1N 120.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 30/0600Z 18.8N 123.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 01/0600Z...DISSIPATED $$ Forecaster Stewart

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Tropical Depression One-E Forecast Discussion Number 2

2019-06-26 04:37:12| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Tue Jun 25 2019 286 WTPZ41 KNHC 260237 TCDEP1 Tropical Depression One-E Discussion Number 2 NWS National Hurricane Center Miami FL EP012019 900 PM MDT Tue Jun 25 2019 The cyclone has not yet acquired well-defined convective banding features and the deep convection is rather fragmented at this time, however microwave imagery shows a fairly well-defined inner circulation structure. The initial intensity is set at 30 kt in accord with Dvorak estimates from TAFB and SAB. Hopefully, we will soon obtain a scatterometer overpass to provide a better estimate of the intensity of the system. The cyclone should move over sufficiently warm waters and within low vertical shear over the next day or so. Therefore some strengthening is forecast until around the 36 hours time frame. Thereafter, increasing south-southwesterly shear, cooler waters, and drier mid-level air should induce weakening. The official intensity forecast is similar to the previous one and very close to the latest model consensus prediction. Based on microwave and geostationary satellite center fixes, a fairly brisk west-northwestward motion, at about 290/13 kt, continues. The primary steering mechanism for the next couple of days will be a mid-level ridge extending westward from northwestern Mexico into the Pacific. The tropical cyclone should gradually slow its forward speed as it nears the western periphery of the ridge. The official track forecast is close to the previous one, and is in agreement with the latest simple and corrected dynamical model consensus solutions. The ECMWF model shows a track at a more southern latitude, but that model's prediction of the cyclone's evolution seems to be unrealistically weak. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 15.6N 106.8W 30 KT 35 MPH 12H 26/1200Z 15.9N 108.9W 35 KT 40 MPH 24H 27/0000Z 16.3N 111.6W 35 KT 40 MPH 36H 27/1200Z 16.8N 113.9W 40 KT 45 MPH 48H 28/0000Z 17.5N 116.0W 35 KT 40 MPH 72H 29/0000Z 18.6N 119.4W 25 KT 30 MPH 96H 30/0000Z 19.4N 122.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 01/0000Z...DISSIPATED $$ Forecaster Pasch

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Tropical Depression One-E Forecast Discussion Number 1

2019-06-25 22:36:11| National Hurricane Center (East Pacific)

Issued at 400 PM CDT Tue Jun 25 2019 000 WTPZ41 KNHC 252036 TCDEP1 Tropical Depression One-E Discussion Number 1 NWS National Hurricane Center Miami FL EP012019 400 PM CDT Tue Jun 25 2019 Convection associated with the area of low pressure located south of the coast of Mexico has become sufficiently well organized today, and visible satellite imagery suggest that the system has acquired a well-defined center. Based on these observations, advisories are being initiated on the first tropical depression of the 2019 eastern Pacific hurricane season. The latest Dvorak T-numbers from TAFB and SAB are 2.0 and 1.5 respectively, and the initial wind speed has been set at 25 kt. The depression is forecast to remain over warm sea surface temperatures and within a low wind shear environment during the next couple of days. Although there is some dry mid-level air to the west of the cyclone, modest strengthening is indicated by most of the intensity guidance, and the NHC foreast follows suit. After 48 hours, increasing south-southwesterly shear and cooler waters are expected to cause weakening, and the system is forecast to become a remnant low in 3 to 4 days. The somewhat uncertain initial motion estimate is 290/13 kt. A mid-level ridge extending from northwestern Mexico into the eastern Pacific should steer the cyclone west-northwestward during the next few days. There is spread in the guidance as to how much latitude the system will gain over the next few days. The ECMWF which does not deepen the system much, if at all, shows a more southern track than the remainder of the guidance. The NHC forecast assumes that the system will strengthen some and shows a more climatological west-northwestward track close to the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 15.2N 105.7W 25 KT 30 MPH 12H 26/0600Z 15.8N 107.7W 30 KT 35 MPH 24H 26/1800Z 16.2N 110.6W 35 KT 40 MPH 36H 27/0600Z 16.7N 113.2W 40 KT 45 MPH 48H 27/1800Z 17.4N 115.5W 35 KT 40 MPH 72H 28/1800Z 18.5N 119.2W 25 KT 30 MPH 96H 29/1800Z 18.8N 122.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 30/1800Z...DISSIPATED $$ Forecaster Brown

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Discussion Slides

2019-06-07 00:25:02| PortlandOnline

PDF Document, 638kbCategory: June 3, 2019 CAG Meeting #2

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