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Hurricane AMANDA Forecast Discussion Number 21

2014-05-27 22:36:39| National Hurricane Center (East Pacific)

Issued at 200 PM PDT TUE MAY 27 2014 000 WTPZ41 KNHC 272035 TCDEP1 HURRICANE AMANDA DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 200 PM PDT TUE MAY 27 2014 Amanda's cloud pattern has deteriorated in organization today. Although the cyclone is producing some very intense convection, the thunderstorms are not particularly well organized, and there is little evidence of banding features. The current intensity estimate is set at 90 kt in agreement with the latest Dvorak estimate from NESDIS SAB - however, this may be generous. The weakening of the hurricane may be partially due to its slow movement, and the resultant upwelling of cooler ocean waters. Although the vertical shear is predicted to diminish over the next day or two, drier air and lower sea surface temperatures are likely to induce continued weakening. The official wind speed forecast is very close to the latest Decay-SHIPS and intensity model consensus guidance. The hurricane continues to plod north-northwestward at 4 kt between a weak mid-level ridge to its northeast and a weak trough to its northwest. Steering currents are forecast to remain weak for the next several days, but most of the track models show the tropical cyclone turning northward and then northeastward over the next couple of days into a slight weakness in the ridge over northwestern Mexico. Late in the forecast period, a northeast- southwest oriented ridge extending across the Baja California peninsula should cause Amanda to turn southwestward. The official track forecast is only slightly west of the previous one and close to the latest dynamical model consensus. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 15.0N 112.6W 90 KT 105 MPH 12H 28/0600Z 15.6N 112.4W 75 KT 85 MPH 24H 28/1800Z 16.4N 112.0W 65 KT 75 MPH 36H 29/0600Z 17.3N 111.4W 55 KT 65 MPH 48H 29/1800Z 18.0N 110.7W 50 KT 60 MPH 72H 30/1800Z 18.0N 111.0W 40 KT 45 MPH 96H 31/1800Z 17.5N 111.5W 30 KT 35 MPH 120H 01/1800Z 17.0N 112.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Pasch

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Hurricane AMANDA Forecast Discussion Number 20

2014-05-27 17:00:57| National Hurricane Center (East Pacific)

Issued at 800 AM PDT TUE MAY 27 2014 000 WTPZ41 KNHC 271500 TCDEP1 HURRICANE AMANDA DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 800 AM PDT TUE MAY 27 2014 Amanda's eye has again disappeared from the infrared and first-light visible imagery from GOES-West this morning. However, microwave imagery from the TRMM and SSMI polar-orbiting satellites still indicated a small, complete eyewall was present. Using a blend of final T and Dvorak current intensity estimates from TAFB and SAB suggests an intensity of 100-105 kt, while the ADT estimate of 125 kt appears to be too high. The initial intensity is set at 105 kt, but this may be slightly too strong if the current deterioration of the convective structure continues. The initial wind radii are primarily based upon a 0518Z ASCAT-A scatterometer pass. The microwave imagery fixes allow for a fairly confident assessment of the initial position and motion of Amanda. The hurricane is moving toward the north-northwest - 340 degrees - at about 5 kt, due to the steering influence of an upper- to mid-level low to its northwest and a ridge to its northeast. These features should continue to slowly advect Amanda toward the north or north-northeast for the next three days or so, before a strong northeast-southwest oriented ridge builds north of the tropical cyclone. That ridge, along with a weakening Amanda being steered by the low-level flow, should result in Amanda turning to the southwest in the latter part of the forecast period. The models are in generally good agreement with this scenario, but differ some on when the turn occurs, and thus how far to the north Amanda reaches. On the extremes, the GFS has Amanda getting farthest to the north at 21N while the UKMET only has the cyclone reaching 17N before the turn occurs. The official forecast is a blend of the farther north TVCE variable consensus technique and the farther south previous official forecast. The CIMSS analysis and the GFS-based SHIPS both indicate southerly vertical shear of about 20 kt affecting Amanda. While the shear is anticipated to diminish quite a bit by all of the dynamical models in about two days, the moisture and instability should decrease significantly at the same time. The dynamical models very quickly weaken Amanda, while the dynamical-statistical guidance shows more gradual weakening. However, it appears that the SSTs being used in SHIPS/LGEM are biased high by about 1 degree C along the track of Amanda, which would suggest that these statistical techniques are somewhat too strong. The official forecast is very similar to the IVCN variable consensus model and the previous advisory. However, if current convective trends continue and the statistical models do indeed turn out to be biased high, then this forecast may be conservative in how quickly Amanda falls apart. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 14.7N 112.3W 105 KT 120 MPH 12H 28/0000Z 15.2N 112.3W 90 KT 105 MPH 24H 28/1200Z 15.8N 111.8W 75 KT 85 MPH 36H 29/0000Z 16.6N 111.2W 60 KT 70 MPH 48H 29/1200Z 17.5N 110.6W 50 KT 60 MPH 72H 30/1200Z 18.5N 110.0W 40 KT 45 MPH 96H 31/1200Z 18.0N 110.5W 30 KT 35 MPH 120H 01/1200Z 17.5N 111.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Landsea

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Hurricane AMANDA Forecast Discussion Number 19

2014-05-27 10:48:28| National Hurricane Center (East Pacific)

Issued at 200 AM PDT TUE MAY 27 2014 000 WTPZ41 KNHC 270848 TCDEP1 HURRICANE AMANDA DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 200 AM PDT TUE MAY 27 2014 Amanda apparently still has some gas in the tank. The hurricane appeared to be succumbing to strong vertical shear on Monday, but its satellite presentation has improved markedly during the past several hours. An eye has reappeared and is completely surrounded by convective tops as cold as -85C. The shear is still affecting the structure, however, with the clouds elongated from south to north. Nonetheless, Dvorak estimates have risen to T6.0/115 kt from TAFB, T5.5/102 kt from SAB, and T6.5/127 kt from the objective ADT. The initial intensity is therefore raised to 110 kt based on a conservative blend of these data. The recent reintensification has resulted in a somewhat significant change to the official intensity forecast. Weakening is expected to resume soon due to strong south to southwesterly shear, which should persist for another 24 hours or so. After that time, however, an upper-level shortwave trough currently to the northwest of Amanda is expected to lift northeastward and dampen, which could leave the hurricane in a slightly more favorable upper-level environment for a few days. Due to the higher initial intensity and the more favorably evolving upper-level pattern, the NHC intensity forecast shows more gradual weakening than before, and Amanda may not become a remnant low until the very end of the forecast period. Despite the adjustment, the updated forecast is near the lower end of the intensity guidance and matches best with the FSU Superensemble. The weakening trend could be even slower if the rest of the intensity models end up being correct. Amanda continues to move slowly north-northwestward...or 340/4 kt... between a weak mid-level ridge over Mexico and a mid-/upper-level trough near 20N128W. As the trough migrates eastward, Amanda is forecast to continue moving slowly northward and then turn northeastward by 48 hours. Once the cyclone weakens, however, weak low-level flow off the coast of Mexico will likely cause it to stall or meander by days 4 and 5. Although there is still a significant amount of spread in the track guidance, nearly all of the models have shifted to the right, with the GFS and ECMWF lying on the eastern edge of the guidance envelope. The NHC track has also been nudged eastward and lies to the right of the multi-model consensus TVCE. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 14.2N 112.2W 110 KT 125 MPH 12H 27/1800Z 14.6N 112.3W 95 KT 110 MPH 24H 28/0600Z 15.1N 112.1W 80 KT 90 MPH 36H 28/1800Z 15.8N 111.6W 65 KT 75 MPH 48H 29/0600Z 16.4N 111.0W 50 KT 60 MPH 72H 30/0600Z 17.5N 110.0W 40 KT 45 MPH 96H 31/0600Z 17.5N 109.5W 35 KT 40 MPH 120H 01/0600Z 17.0N 110.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg

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Hurricane AMANDA Forecast Discussion Number 18

2014-05-27 04:35:56| National Hurricane Center (East Pacific)

Issued at 800 PM PDT MON MAY 26 2014 000 WTPZ41 KNHC 270235 TCDEP1 HURRICANE AMANDA DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 800 PM PDT MON MAY 26 2014 Amanda's cloud pattern had been reasonably well organized during the day, with the cyclone maintaining a small Central Dense Overcast and an intermittent but faint eye. The eye has since disappeared and the convective structure has become increasingly less symmetric, presumably as a consequence of an increase in southerly vertical wind shear. The cloud pattern has also recently become elongated poleward, with little to no outflow noted to the south. Using a blend of Dvorak T- and CI numbers and recent satellite trends...the advisory wind speed is reduced to 90 kt. Center fixes indicate that Amanda has moved somewhat erratically during the day...but smoothing through these yields an initial motion of 340/04. The cyclone is embedded in a region of weak steering flow between a mid-level ridge over the Gulf of Mexico and a mid- to upper-level trough to the west. This pattern should steer the cyclone slowly northward during the next couple of days. After that time, the forecast becomes more challenging as the model spread increases significantly. The GFS forecasts Amanda to remain a deeper cyclone longer and therefore moves it much farther northeast, while the ECMWF shows the cyclone decoupling sooner and interacting with a disturbance to the its east. As a result, Amanda or its remnants in the ECMWF solution move generally eastward without gaining much latitude. Given the uncertainty, the official forecast is close to the multi-model consensus TVCE and a little to the east of the previous forecast beyond 36 hours. Global models show the shear at its worst during the next 24 hours and then slowly decreasing as the mid- to upper-level trough affecting the cyclone lifts out. Even though upper-level winds are forecast to become anticyclonic late in the period...what remains of the Amanda should be moving over cooler waters and within a region of substantially drier and more stable air in the wake of the aforementioned trough. Thus, it would seem that the shear debilitates Amanda and the other negative factors cause the cyclone to degenerate into a remnant low. The official forecast is lower than the previous one and is a blend of the multi-model intensity consensus ICON and LGEM. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 13.7N 111.9W 90 KT 105 MPH 12H 27/1200Z 14.2N 112.1W 80 KT 90 MPH 24H 28/0000Z 14.9N 112.2W 65 KT 75 MPH 36H 28/1200Z 15.4N 112.2W 50 KT 60 MPH 48H 29/0000Z 15.9N 112.0W 35 KT 40 MPH 72H 30/0000Z 16.5N 111.5W 30 KT 35 MPH 96H 31/0000Z 17.0N 111.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 01/0000Z 16.9N 111.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Kimberlain

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Hurricane AMANDA Forecast Discussion Number 17

2014-05-26 22:58:52| National Hurricane Center (East Pacific)

Issued at 200 PM PDT MON MAY 26 2014 000 WTPZ41 KNHC 262058 TCDEP1 HURRICANE AMANDA DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 200 PM PDT MON MAY 26 2014 After significant erosion of the deep convection in the southern portion of the eyewall, a resurgence of convective development has occurred in the past couple of hours, including the redevelopment of the CDO feature and a cloud-filled eye. However, an average of all available satellite intensity estimates indicates that Amanda has still weakened and is now a 105-kt category 3 hurricane. A 12-hour average motion of 335/04 kt was used for the advisory motion, in spite of the many wobbles in the track during the past few hours. Although the model guidance isn't quite the proverbial squashed spider pattern that typically suggests a slow and erratic motion, it isn't far from it. Amanda is expected to move slowly northward into a broad weakness in the subtropical ridge to the north of the cyclone during the next few days, during which time the steering currents are forecast to collapse. While the steering currents erode, Amanda is also forecast to become a significantly weaker and more shallow cyclone during that time, resulting in the cyclone meandering south of Socorro Island as a remnant low by Day 5, if not sooner. The official forecast track remains close to a blend of the consensus model TVCE and the FSSE model. Deep-layer shear of more than 20 kt is expected to continue to affect Amanda for the next 24 hours or so, resulting in steady to rapid weakening during the forecast period. The NHC intensity forecast is similar to the previous advisory, and remains close to the intensity consensus model IVCN. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 13.4N 111.8W 105 KT 120 MPH 12H 27/0600Z 14.0N 112.0W 90 KT 105 MPH 24H 27/1800Z 14.8N 112.2W 75 KT 85 MPH 36H 28/0600Z 15.4N 112.3W 60 KT 70 MPH 48H 28/1800Z 15.9N 112.2W 45 KT 50 MPH 72H 29/1800Z 16.4N 111.9W 30 KT 35 MPH 96H 30/1800Z 16.7N 111.7W 25 KT 30 MPH 120H 31/1800Z 16.7N 112.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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