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Tropical Storm Hector Forecast Discussion Number 2

2018-08-01 04:32:41| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Tue Jul 31 2018 224 WTPZ45 KNHC 010232 TCDEP5 Tropical Storm Hector Discussion Number 2 NWS National Hurricane Center Miami FL EP102018 800 PM PDT Tue Jul 31 2018 Deep convection associated with the tropical cyclone has continued to become better organized since the previous advisory with an increase in banding over the western and southern portions of the circulation. As a result, satellite intensity estimates have increased to T2.5 on the Dvorak scale, so the initial wind speed has been increased to 35 kt. Hector becomes the eighth named storm of the 2018 eastern North Pacific hurricane season. Hector is forecast to traverse warm SSTs and remain within a favorable upper-level wind pattern during the next day or so which should result in steady strengthening. Some moderate northeasterly shear could temper the rate of intensification in 36-48 h, but the intensity guidance is generally more aggressive this cycle. The NHC intensity forecast calls for a faster rate of strengthening early in the forecast period, and brings Hector to hurricane status in a couple of days, which is in line with most of the intensity guidance. The updated official forecast also indicates a slightly higher peak intensity, but it is not as high as the dynamical model guidance and the ICON intensity consensus model in deference to the previous NHC advisory. Recent satellite fixes indicate that Hector is moving west- northwestward or 285/12 kt. A strong deep-layer ridge to the north of the tropical storm is expected to keep the system on a generally west-northwestward to westward motion throughout the forecast period. The track guidance is in good agreement on this scenario, but there are some differences in the predicted forward speed of the cyclone. The ECMWF depicts a faster westward motion while the GFS, GFS ensemble mean, and HWRF show a somewhat slower speed. The new NHC track forecast is a little faster than the previous official forecast, but is slower than most of the consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 13.0N 118.2W 35 KT 40 MPH 12H 01/1200Z 13.4N 119.9W 45 KT 50 MPH 24H 02/0000Z 13.8N 122.0W 55 KT 65 MPH 36H 02/1200Z 13.9N 124.0W 60 KT 70 MPH 48H 03/0000Z 13.9N 126.1W 65 KT 75 MPH 72H 04/0000Z 13.8N 130.1W 70 KT 80 MPH 96H 05/0000Z 13.7N 134.0W 75 KT 85 MPH 120H 06/0000Z 13.7N 138.0W 70 KT 80 MPH $$ Forecaster Brown

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Tropical Depression Ten-E Forecast Discussion Number 1

2018-07-31 22:39:41| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Tue Jul 31 2018 142 WTPZ45 KNHC 312039 TCDEP5 Tropical Depression Ten-E Discussion Number 1 NWS National Hurricane Center Miami FL EP102018 200 PM PDT Tue Jul 31 2018 The broad low pressure system and area of disturbed weather that the NHC has been tracking for the past several days has finally become well-defined enough and has acquired sufficient organized deep convection near the center to be classified as a tropical depression. The low-level center is estimated to be just inside the southeastern edge of the figure-6 cloud mass based on conventional and microwave satellite fix data. The initial intensity estimate of 30 kt is based on Dvorak satellite classifications of T2.0/30 kt from TAFB and T2.5/35 kt from SAB, along with uncontaminated 30-kt winds in a 1634 UTC Scatsat-1 scatterometer pass. The initial motion estimate is west-northwestward or 290/11 kt. A deep-layer ridge to the north of the depression should keep the tropical cyclone moving toward the west-northwest for the next 48 hours or so, followed by a turn toward the west thereafter due to the ridge building slightly southward on days 3-5. The NHC track forecast closely follows a blend of the consensus models TVCN and HCCA since this is the first forecast on this system. Although the comma-shaped cloud pattern is suggestive of a slightly stronger system, microwave imagery and the Scatsat-1 pass indicate that the circulation envelope is elongated northeast-to-southwest, and that westerly winds likely only extend about 30 n mi to the south of the center. Due to the cyclone's irregular shape, the peak winds are being held lower than the Dvorak T2.5 data-T numbers. Visible satellite imagery shows the tops of shallow convection in the eastern semicircle blowing off toward the west, which is indicative of modest mid-level shear undercutting the favorable high-level cirrus outflow layer. This mid-level flow is also likely producing some intrusions of dry air, a negative condition that should act to inhibit inner-core convective development in the short term. These aforementioned unfavorable environmental conditions, in conjunction with the irregular shape of the cyclone's circulation, should result in only slow strengthening for the next 48 hours or so, despite the very favorable deep-layer, low vertical wind shear environment. In the 48-72 h period, both the GFS and ECMWF models are forecasting the shear to increase to near 15 kt, which should act to maintain only slow development. By days 4 and 5, the shear is forecast to abate, and the cyclone is forecast to become a hurricane by 120 hours. The intensity forecast follows the trend of the HCCA and IVCN intensity consensus models, but is slightly higher due to the HMON model showing immediate weakening, which is pulling down the consensus intensity forecasts. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 12.7N 116.7W 30 KT 35 MPH 12H 01/0600Z 13.1N 118.4W 35 KT 40 MPH 24H 01/1800Z 13.6N 120.3W 40 KT 45 MPH 36H 02/0600Z 13.8N 122.4W 45 KT 50 MPH 48H 02/1800Z 14.0N 124.6W 50 KT 60 MPH 72H 03/1800Z 13.8N 128.7W 55 KT 65 MPH 96H 04/1800Z 13.7N 132.6W 60 KT 70 MPH 120H 05/1800Z 13.6N 136.7W 65 KT 75 MPH $$ Forecaster Stewart

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Post-Tropical Cyclone Gilma Forecast Discussion Number 13

2018-07-29 22:52:27| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sun Jul 29 2018 076 WTPZ43 KNHC 292052 TCDEP3 Post-Tropical Cyclone Gilma Discussion Number 13 NWS National Hurricane Center Miami FL EP082018 200 PM PDT Sun Jul 29 2018 Gilma has lacked organized deep convection near the center for at least 12 hours now. Although there has been a cluster of thunderstorms lingering about 90 n mi southeast of the exposed center, this convection has been pulling away from the system and lacks sufficient organization necessary for a tropical cyclone. Therefore, this is the last advisory issued by the National Hurricane Center on Gilma. Very strong west-northwesterly shear is expected to continue during the next few days. These hostile winds combined with marginal SSTs and dry air should cause the remnant low to degenerate into a trough in 36 to 48 hours. The remnant low is moving westward at 13 kt steered by the low-level flow on the south side of a ridge, and it should cross into the Central Pacific basin shortly. This general motion is expected to continue until the system dissipates. For additional information on the remnant low please see High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFEPI, WMO header FZPN02 KWBC, and on the web at https://ocean.weather.gov/shtml/NFDHSFEPI.shtml. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 16.2N 139.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 12H 30/0600Z 16.2N 141.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 30/1800Z 16.1N 143.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 31/0600Z 15.9N 146.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 31/1800Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Depression Gilma Forecast Discussion Number 12

2018-07-29 16:41:24| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sun Jul 29 2018 256 WTPZ43 KNHC 291441 TCDEP3 Tropical Depression Gilma Discussion Number 12 NWS National Hurricane Center Miami FL EP082018 800 AM PDT Sun Jul 29 2018 Gilma is on its way in becoming a remnant low. Very strong west-northwesterly shear has pushed all of the associated convection well away from the center, leaving a completely exposed low-level swirl. The initial intensity is held at 30 kt, in agreement with a blend of the Dvorak Final T- and CI-numbers from TAFB and SAB. Now that Gilma is located to the west of an upper-level trough axis, strong west-northwesterly shear is expected to continue. These hostile winds aloft, plus marginal SSTs and dry air, should cause Gilma to become a remnant low later today and ultimately degenerate into a trough in 2 to 3 days. The depression is moving westward at 12 kt, steered by the flow on the south side of a low- to mid-level ridge. This general motion with a slight decrease in forward speed is expected until the system dissipates. Little change was made to the previous NHC track forecast, and this one lies near the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 15.9N 138.5W 30 KT 35 MPH 12H 30/0000Z 16.0N 140.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 30/1200Z 15.9N 142.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 31/0000Z 15.7N 144.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 31/1200Z 15.5N 147.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 01/1200Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Depression Gilma Forecast Discussion Number 11

2018-07-29 10:37:52| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sun Jul 29 2018 728 WTPZ43 KNHC 290837 TCDEP3 Tropical Depression Gilma Discussion Number 11 NWS National Hurricane Center Miami FL EP082018 200 AM PDT Sun Jul 29 2018 Gilma continues to generate convection to the east of the exposed low-level center despite the ongoing 30 kt or more of westerly vertical wind shear. Satellite intensity estimates are in the 30-40 kt range, and the initial intensity will be held at 30 kt based on these data and the unchanged organization since the last advisory. The initial motion is now 280/13. Gilma is expected to move westward and eventually south of westward during the next 2-3 days in the low-level flow associated with the subtropical ridge to the north. There has been a slight southward shift of the guidance since the last advisory, and the forecast track is thus nudged a little southward. The new track continues to lie close to the various consensus models. An upper-level trough located over the cyclone has been providing support for the central convection to persist despite the shear. The large-scale models forecast that Gilma will move west of the trough axis during the next 12-24 h, which will expose the tropical cyclone to 40-50 kt northwesterly upper-level winds and an environment of upper-level convergence. These developments should bring an end to the central convection and cause Gilma to decay to a remnant low. The remnants of the cyclone should weaken to a trough between 48-72 h as indicated by the large-scale models. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 16.1N 137.0W 30 KT 35 MPH 12H 29/1800Z 16.2N 138.6W 30 KT 35 MPH 24H 30/0600Z 16.1N 140.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 30/1800Z 16.0N 143.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 31/0600Z 15.8N 145.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 01/0600Z...DISSIPATED $$ Forecaster Beven

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