Home › discussion
 

Keywords :   


Tag: discussion

Tropical Storm FIONA Forecast Discussion Number 5

2016-08-18 04:44:45| National Hurricane Center (Atlantic)

Issued at 1100 PM AST WED AUG 17 2016 000 WTNT41 KNHC 180244 TCDAT1 TROPICAL STORM FIONA DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 1100 PM AST WED AUG 17 2016 For a time late this afternoon, it seemed that Fiona might lose all its deep convection. However, a new burst developed around 2300 UTC and has persisted since that time. An 0026 UTC ASCAT-B pass revealed that the cyclone is still producing a small area of tropical-storm-force winds, and the intensity remains 35 kt. Fiona has a tough road ahead. Vertical shear right now is relatively low, but it is expected to begin increasing within the next 24 hours and then become belligerent out of the southwest by days 3 and 4. In addition, the cyclone is surrounded by dry air, and any negative impacts that the dry air is already having on the convection is likely to be compounded once the shear increases in a few days. With the exception of the GFDL, which makes Fiona a hurricane by the end of the forecast period, the rest of the intensity models respond to the unfavorable environment by showing relatively little strengthening. The NHC forecast follows this same thinking, and it shows Fiona only modestly strengthening during the next 36 hours, with some weakening probable by day 3. Based on the latest intensity guidance, the new NHC forecast has been adjusted downward from the previous forecast, but it still lies above the consensus at most forecast times. The recent ASCAT data helped to fix the center, and the initial motion estimate is now west-northwestward, or 300/14 kt. A break in the mid-tropospheric ridge to the north of Fiona is expected to to migrate westward during the next few days, but the cyclone's shallow nature is expected to help maintain a west-northwestward motion for much of the forecast period. The bulk of the track models are tightly clustered on such a heading. However, the GFDL (which makes Fiona hurricane) shows a sharp northward turn, while the HWRF (which essentially shows no intensification) takes a much more southern track. Since these two scenarios appear to cancel each other out, the NHC official forecast closely follows the consensus models, requiring a westward adjustment to the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 15.5N 39.0W 35 KT 40 MPH 12H 18/1200Z 16.3N 40.4W 35 KT 40 MPH 24H 19/0000Z 17.1N 41.9W 40 KT 45 MPH 36H 19/1200Z 17.8N 43.5W 45 KT 50 MPH 48H 20/0000Z 18.6N 45.2W 45 KT 50 MPH 72H 21/0000Z 20.6N 49.1W 40 KT 45 MPH 96H 22/0000Z 22.5N 53.0W 40 KT 45 MPH 120H 23/0000Z 24.5N 57.0W 40 KT 45 MPH $$ Forecaster Berg

Tags: number discussion storm tropical

 

Tropical Storm FIONA Forecast Discussion Number 4

2016-08-17 22:42:23| National Hurricane Center (Atlantic)

Issued at 500 PM AST WED AUG 17 2016 000 WTNT41 KNHC 172042 TCDAT1 TROPICAL STORM FIONA DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 500 PM AST WED AUG 17 2016 During the past 6 hours, the tropical cyclone has made a transition from a large outer banding pattern to more of a CDO-type feature. Also, a 1635Z SSMI overpass confirmed the tight inner-core structure noted in the two earlier ASCAT passes. Dvorak satellite intensity estimates are T2.5/35 kt from TAFB and SAB, and a 1225Z ASCAT-A overpass indicated winds of near 35 kt at that time. Based on these data, the initial intensity is increased to 35 kt and the cyclone is upgraded to Tropical Storm Fiona. The initial motion estimate is 305/14 kt. The latest model guidance has come into much better agreement with the previous track forecast, with the GFS model shifting a little farther south and the ECMWF making a significant shift to the north due to that model not weakening Fiona as much now as compared to previous forecast cycles. These model changes have resulted in a northward shift in the consensus models TVCN and GFEX. Given the much better agreement in the NHC model guidance, the new track forecast was only shifted slightly southward of the previous advisory track after 72 hours in order to move closer to the consensus models. There are no significant changes to the previous intensity forecast. Fiona is a compact tropical cyclone with a radius of maximum winds of 15 nmi or less, which makes the storm susceptible to sharp fluctuations in intensity. The aforementioned SSMI satellite pass also indicated that the small inner-core region of Fiona now appears to be insulated from the very dry mid-level air that had earlier eroded the cyclone's convection. That, along with low shear conditions and marginal SSTs near 27C, should allow for some gradual strengthening for the next 36-48 hours, assuming that the cyclone can mix out any occasional intrusions of dry air. By 72 hours, the vertical shear is forecast to increase to around 20 kt from the southwest, which should act to arrest the intensification process and perhaps even induce some slight weakening. However, by 96 hours and beyond, the shear is forecast to steadily decrease when the cyclone will be moving over SSTs greater than 28C. These conditions could allow for the compact cyclone to maintain a steady intensity despite being embedded in mid-level humidity values of near 50 percent. The official intensity forecast is similar to the previous advisory and closely follows the intensity consensus model IVCN through 48 hours, and then lies just below the Decay-SHIPS model at 72-120 hours. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 15.1N 37.8W 35 KT 40 MPH 12H 18/0600Z 16.0N 39.0W 40 KT 45 MPH 24H 18/1800Z 17.0N 40.6W 45 KT 50 MPH 36H 19/0600Z 17.8N 42.1W 50 KT 60 MPH 48H 19/1800Z 18.7N 43.8W 50 KT 60 MPH 72H 20/1800Z 20.3N 47.4W 45 KT 50 MPH 96H 21/1800Z 22.6N 51.3W 45 KT 50 MPH 120H 22/1800Z 24.6N 55.0W 45 KT 50 MPH $$ Forecaster Stewart

Tags: number discussion storm tropical

 
 

Tropical Depression SIX Forecast Discussion Number 3

2016-08-17 16:36:15| National Hurricane Center (Atlantic)

Issued at 1100 AM AST WED AUG 17 2016 000 WTNT41 KNHC 171436 TCDAT1 TROPICAL DEPRESSION SIX DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 1100 AM AST WED AUG 17 2016 The depression's overall cloud pattern and low-level wind field have continued to improve, although cloud tops have warmed considerably near the center since the previous advisory. An 1139Z ASCAT-B overpass showed a well-defined low-level circulation center with a tight radius of maximum winds of only 10-15 nmi. Although there were a few vectors near tropical storm force, and satellite estimates at 1200Z were T2.5/35 kt from TAFB and SAB, the intensity is being maintained at 30 kt for this advisory due to the sharp decrease in deep convection near the center during the past few hours. The modest northeasterly vertical wind shear across the cyclone is forecast to weaken and veer to the southeast during the next 12 hours, and remain less than 10 kt for the next 36-48 hours, which typically favors strengthening. Sea-surface temperatures just below 27C are marginal for intensification and the small cyclone will be moving through dry mid-level air with humidity values dropping below 50 percent by 48 hours and beyond, conditions that are generally not conducive for significant strengthening. But given the tight inner-core wind field noted in recent ASCAT data, the cyclone is expected to be able to mix out any dry air intrusions and slowly strengthen for about the next 48 hours. By 72 hours and beyond, however, increasing southwesterly to westerly wind shear is expected to induce gradual weakening. The official intensity forecast is similar to the previous advisory and closely follows the intensity consensus model IVCN. The initial motion estimate is 300 /13 kt, based primarily on microwave and scatterometer fixes. The NHC model guidance is in good agreement on the cyclone moving west-northwestward to northwestward toward a weakness in the Bermuda-Azores ridge for the next 48 hours or so. After that, however, there is significant divergence in the models with the GFDL, GFS, and GFS-ensemble mean models taking a stronger and more vertically deep cyclone more toward the northwest, whereas the HWRF, UKMET, NAVGEM, and ECMWF models show a weaker and shallower cyclone turning more westward and moving along the southern periphery of the low-level ridge. As a result, the forecast track depends heavily on the strength and vertical structure of the cyclone. The new NHC forecast track is a little to the south or left of the previous advisory, but not nearly as far south as the ECMWF model due to expectations that the cyclone will not weaken nearly as much as that model is indicating. The forecast wind radii were decreased somewhat based on the smaller wind field depicted in recent ASCAT data. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 14.0N 36.4W 30 KT 35 MPH 12H 18/0000Z 14.9N 37.7W 35 KT 40 MPH 24H 18/1200Z 16.0N 39.3W 40 KT 45 MPH 36H 19/0000Z 17.0N 40.7W 45 KT 50 MPH 48H 19/1200Z 17.9N 42.3W 50 KT 60 MPH 72H 20/1200Z 19.6N 45.9W 45 KT 50 MPH 96H 21/1200Z 21.8N 49.8W 40 KT 45 MPH 120H 22/1200Z 23.9N 53.4W 35 KT 40 MPH $$ Forecaster Stewart

Tags: number discussion tropical depression

 

Tropical Depression SIX Forecast Discussion Number 2

2016-08-17 10:37:41| National Hurricane Center (Atlantic)

Issued at 500 AM AST WED AUG 17 2016 000 WTNT41 KNHC 170837 TCDAT1 TROPICAL DEPRESSION SIX DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 500 AM AST WED AUG 17 2016 The depression's cloud pattern is gradually becoming better organized. It consists of a central mass of deep convection and a newly formed band over the northern half of the circulation. The low-level center appears to still be located near the northeastern edge of the main convective mass, likely due to some northeasterly shear. Satellite classifications are T2.0 from TAFB and SAB, and support maintaining the initial intensity estimate of 30 kt. The northeasterly shear is forecast to decrease while the cyclone moves over marginally warm waters during the next 24 to 36 hours. These two factors should favor some intensification during this time frame. However, the global models, and the ECMWF in particular, show the cyclone moving into a much drier environment after 48 hours and encountering strong southwesterly shear in association with a mid- to upper-level trough. Thus weakening is forecast to begin by day 3 despite the cyclone's trek over warmer waters, and there is the possibility that the system could degenerate into a remnant low by day 4 or 5 as depicted in the ECMWF. The new NHC intensity forecast is somewhat higher than the previous one and the multi- model consensus in the short term but lower later in the forecast period and a little below most of the guidance. The depression has been responding to a weakness in the subtropical ridge between 40w and 50w by moving on a northwesterly track, and the initial motion estimate is 305/13. The track guidance remains split into two distinct camps, with GFS-based deterministic models and GFS ensemble members showing a deeper system moving more poleward. The ECMWF and its ensemble solutions are much farther to the south as a result of the model's forecast of a weaker, shallower system moving on a more westerly course. Based on the assumption of a weaker system, the NHC track forecast is adjusted toward the ECMWF solution, and is well south of the previous one and a little to the left of the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 13.2N 35.2W 30 KT 35 MPH 12H 17/1800Z 14.3N 36.8W 40 KT 45 MPH 24H 18/0600Z 15.5N 38.3W 45 KT 50 MPH 36H 18/1800Z 16.8N 39.9W 50 KT 60 MPH 48H 19/0600Z 17.8N 41.4W 50 KT 60 MPH 72H 20/0600Z 19.2N 44.7W 45 KT 50 MPH 96H 21/0600Z 21.6N 48.9W 40 KT 45 MPH 120H 22/0600Z 23.6N 52.3W 35 KT 40 MPH $$ Forecaster Kimberlain

Tags: number discussion tropical depression

 

Tropical Depression SIX Forecast Discussion Number 1

2016-08-17 04:48:08| National Hurricane Center (Atlantic)

Issued at 1100 PM AST TUE AUG 16 2016 000 WTNT41 KNHC 170248 TCDAT1 TROPICAL DEPRESSION SIX DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062016 1100 PM AST TUE AUG 16 2016 Convective activity associated with the tropical wave and associated low pressure area over the tropical Atlantic has become more concentrated and better organized this evening, and a recent ASCAT overpass indicates that the circulation has become better defined. Based on these data, this system has been designated a tropical depression, and advisories are being initiated at this time. The initial wind speed of 30 kt is supported by the scatterometer data. Some northeasterly shear is affecting the depression, with the center located near the northeastern edge of the primary convective mass. The shear is forecast to decrease tonight and remain low during the next couple of days which favors strengthening. However, dry mid-level air is lurking just to the north of the depression, and intrusions of this unfavorable airmass could arrest development. The NHC forecast shows gradual strengthening during the next couple of days, but it is on the lower side of the guidance, closest to the LGEM and intensity consensus. Later in the forecast period, increasing southwesterly shear being produced by a mid- to upper-level trough over the central Atlantic is likely to weaken the tropical cyclone. The initial motion estimate is a somewhat uncertain 310/12 kt. The depression is forecast to move generally northwestward into a weakness in the subtropical ridge over the central Atlantic. The track guidance is in relatively good agreement through 48 hours, but there is a large spread between the GFS-based guidance and the ECMWF later in the period. The ECMWF and the majority of its ensemble members depict a much weaker and shallower cyclone that turns west-northwestward in the low-level flow after 48 hours. On the other hand, the GFS, GFS ensemble mean, GFDL, and HWRF take a stronger cyclone more poleward. For now, the NHC track is between these two distinct solutions, and is located just south of the multi-model consensus at days 4 and 5. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 12.6N 34.1W 30 KT 35 MPH 12H 17/1200Z 13.7N 35.6W 35 KT 40 MPH 24H 18/0000Z 15.2N 37.2W 40 KT 45 MPH 36H 18/1200Z 16.8N 38.8W 45 KT 50 MPH 48H 19/0000Z 18.1N 40.2W 50 KT 60 MPH 72H 20/0000Z 20.0N 43.2W 50 KT 60 MPH 96H 21/0000Z 22.5N 46.5W 45 KT 50 MPH 120H 22/0000Z 25.0N 50.0W 40 KT 45 MPH $$ Forecaster Brown

Tags: number discussion tropical depression

 

Sites : [856] [857] [858] [859] [860] [861] [862] [863] [864] [865] [866] [867] [868] [869] [870] [871] [872] [873] [874] [875] next »