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Tropical Storm AMANDA Forecast Discussion Number 26

2014-05-29 04:31:40| National Hurricane Center (East Pacific)

Issued at 800 PM PDT WED MAY 28 2014 000 WTPZ41 KNHC 290231 TCDEP1 TROPICAL STORM AMANDA DISCUSSION NUMBER 26 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 800 PM PDT WED MAY 28 2014 The cloud tops of Amanda have been warming during the past few hours with almost no deep convection near the center. Although a well-defined mid-level center is apparent on the latest satellite imagery, this feature is well to the northeast of the low-level circulation as indicated by ASCAT data and a recent SSMI/S pass. Based on the current satellite trends, the initial intensity is lowered to 40 kt, a bit below the recent Dvorak estimates. The microwave data show that Amanda is moving to the northeast at a little slower pace of about 5 kt. This motion should continue on Thursday ahead of a mid-level trough. This trough is expected to moving away from Amanda by Friday, which would leave the storm in light steering currents. After that time, the weakened storm will probably turn to the west and west-southwest as a low- to mid-level ridge builds over the eastern Pacific. There have not been any significant changes to the guidance, and the latest NHC forecast is very close to the previous one. Amanda should continue to weaken for the next couple of days due to moderate shear, dry air aloft and marginal SSTs. While the shear is forecast to weaken some in a day or so, the storm will likely have entrained a significant amount of dry air by then, and it probably won't be able to take advantage of the decreased shear. The cyclone should become a remnant low in a couple of days due to these marginal environment conditions. Most of the guidance shows steady weakening and the official NHC prediction follows suit, at or below the intensity consensus throughout the period. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 16.3N 111.3W 40 KT 45 MPH 12H 29/1200Z 16.7N 110.7W 35 KT 40 MPH 24H 30/0000Z 17.2N 109.7W 30 KT 35 MPH 36H 30/1200Z 17.5N 109.0W 25 KT 30 MPH 48H 31/0000Z 17.6N 109.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 01/0000Z 17.3N 110.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 02/0000Z 16.5N 111.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 03/0000Z...DISSIPATED $$ Forecaster Blake

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Tropical Storm AMANDA Forecast Discussion Number 25

2014-05-28 22:37:42| National Hurricane Center (East Pacific)

Issued at 200 PM PDT WED MAY 28 2014 000 WTPZ41 KNHC 282037 TCDEP1 TROPICAL STORM AMANDA DISCUSSION NUMBER 25 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 200 PM PDT WED MAY 28 2014 Amanda continues to gradually lose strength. Deep convection has decreased in coverage during the last several hours, and the cloud tops are not as cold as they were this morning. Dvorak Final T-numbers were 3.0/45 kt and 3.5/55 kt from SAB and TAFB, respectively. In addition, an ASCAT-B overpass at 1642 UTC showed maximum reliable winds in the 45-50 kt range. Based on these data, the initial intensity is lowered slightly to 50 kt. The low-level center of Amanda, which appeared somewhat elongated in the scatterometer pass, remains near the southern edge of the main area of thunderstorms. This asymmetric cloud pattern is due to about 15 to 20 kt of south-southwesterly shear. Slow weakening is expected to remain the theme during the next few days due to the combination of shear, dry air, and cooler water along the forecast track. The NHC intensity forecast is very similar to the previous one and in line with most of the guidance. The storm is moving a little faster to the northeast, with the latest initial motion estimate being 035/7. A mid- to upper-level trough to the west of Amanda is expected to keep the cyclone moving northeastward or north-northeastward during the next day or two. After that time, the weakening system is expected to reverse its course and turn southwestward when a low- to mid-level ridge builds to its north. Only slight changes were made to the previous official track forecast and it lies fairly close to the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 15.8N 111.6W 50 KT 60 MPH 12H 29/0600Z 16.3N 110.8W 45 KT 50 MPH 24H 29/1800Z 16.9N 109.7W 40 KT 45 MPH 36H 30/0600Z 17.4N 108.7W 35 KT 40 MPH 48H 30/1800Z 17.7N 108.3W 30 KT 35 MPH 72H 31/1800Z 17.6N 109.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 01/1800Z 16.7N 110.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 02/1800Z 16.0N 112.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

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Tropical Storm AMANDA Forecast Discussion Number 24

2014-05-28 16:32:01| National Hurricane Center (East Pacific)

Issued at 800 AM PDT WED MAY 28 2014 000 WTPZ41 KNHC 281431 TCDEP1 TROPICAL STORM AMANDA DISCUSSION NUMBER 24 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 800 AM PDT WED MAY 28 2014 Although Amanda is producing a considerable amount of deep convection, with cloud tops as cold as -85 C, the cloud pattern lacks organization. Microwave images show that the low-level center is located near the southern edge of the convective area, indicative of the continued influence of southerly shear. The latest Dvorak classifications have decreased slightly, and support lowering the initial wind speed to 55 kt. Vertical cross sections from the GFS model show a pronounced south to north tilt of the vortex due to the shear. Since the environmental winds are not expected to change much during the next 24 hours, additional weakening is anticipated. Even though the shear is forecast to lessen on Thursday, Amanda is expected to continue to lose strength due to dry air entrainment and lower sea surface temperatures along the forecast track. The NHC intensity forecast follows the trend in the guidance and calls for Amanda to become a remnant low in a few days. The tropical storm is moving slowly northeastward in the flow between a trough to its west and a ridge to its east over Mexico. This continued motion, with some increase in forward speed, is expected during the next day or two. After that time, however, Amanda is forecast to reverse its course and move slowly southwestward when a low- to mid-level ridge builds to the north of the weakening system. The NHC track forecast is close to the multi-model consensus, and not too far from the previous official track forecast. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 15.0N 112.0W 55 KT 65 MPH 12H 29/0000Z 15.5N 111.4W 45 KT 50 MPH 24H 29/1200Z 16.3N 110.2W 40 KT 45 MPH 36H 30/0000Z 17.1N 109.2W 35 KT 40 MPH 48H 30/1200Z 17.5N 108.7W 30 KT 35 MPH 72H 31/1200Z 17.7N 109.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 01/1200Z 17.0N 110.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 02/1200Z 16.0N 111.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

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Tropical Storm AMANDA Forecast Discussion Number 23

2014-05-28 10:35:01| National Hurricane Center (East Pacific)

Issued at 200 AM PDT WED MAY 28 2014 000 WTPZ41 KNHC 280834 TCDEP1 TROPICAL STORM AMANDA DISCUSSION NUMBER 23 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 200 AM PDT WED MAY 28 2014 A 0457 UTC AMSU pass confirmed that Amanda is a sheared tropical storm, with the low-level center displaced to the south of the deep convection due to about 15 kt of southerly shear. The convection itself increased beginning around 0100 UTC, and now the center is located beneath the cirrus canopy. The initial intensity is held at 60 kt based mainly on SAB's Dvorak classification of T3.5/4.0 using a shear pattern. Modest south to southwesterly shear is expected to continue affecting Amanda for the next 24-36 hours. The shear could relax somewhat after 36 hours, but Amanda will have moved into a less favorable thermodynamic environment by that time. Therefore, gradual weakening is expected, and Amanda is likely to degenerate to a remnant low in about 3 days. The NHC official forecast is unchanged from the previous advisory and is fairly close to the intensity consensus IVCN. Fixes based on microwave data indicate that Amanda's center began meandering and drifting eastward during the past 12 hours. The initial motion is 050/2 kt, but that estimate is highly uncertain. The steering pattern around Amanda is complicated at the moment. An elongated mid-level ridge extends from the Four Corners region of the U.S. southeastward along the length of Mexico, while a broad mid-level trough covers much of the area west of the Baja California peninsula. These features should push Amanda slowly northeastward during the next 48 hours while the cyclone still has some vertical coherency. Once it becomes a remnant low, Amanda will be located in very weak low-level flow and will likely meander or drift southwestward on days 3 through 5. The new NHC track forecast is farther east than the previous forecast due to the relocated initial position. It is not, however, quite as far east as the GFS, ECMWF, or multi-model consensus TVCE. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 14.6N 112.4W 60 KT 70 MPH 12H 28/1800Z 15.0N 111.9W 50 KT 60 MPH 24H 29/0600Z 15.8N 110.9W 40 KT 45 MPH 36H 29/1800Z 16.6N 109.9W 35 KT 40 MPH 48H 30/0600Z 17.2N 109.0W 30 KT 35 MPH 72H 31/0600Z 17.5N 109.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 01/0600Z 17.0N 110.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 02/0600Z 16.0N 110.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg

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Tropical Storm AMANDA Forecast Discussion Number 22

2014-05-28 04:38:33| National Hurricane Center (East Pacific)

Issued at 800 PM PDT TUE MAY 27 2014 000 WTPZ41 KNHC 280238 TCDEP1 TROPICAL STORM AMANDA DISCUSSION NUMBER 22 NWS NATIONAL HURRICANE CENTER MIAMI FL EP012014 800 PM PDT TUE MAY 27 2014 Amanda's cloud pattern continues to lose organization. Several microwave overpasses during the past 6 to 8 hours show that the center of the cyclone is exposed to the south of the nearest deep convection and is located farther south than previous estimated. Late-afternoon visible imagery confirmed these findings, with geostationary imagery also showing the convection warming and shrinking in coverage. The degradation in organization has resulted in a significant decrease of satellite intensity estimates since this afternoon. The initial intensity is somewhat uncertain since the Dvorak technique does not work well for rapidly weakening cyclones but is reduced to 60 kt based on a blend of T- and CI numbers from TAFB and NESDIS SAB. Additional weakening is likely as south-southwesterly shear, the entrainment of drier and more stable air, and a cooler ocean surface take their toll on Amanda. Even though the shear is forecast to decrease in 24 to 36 hours, it appears that it will be too late for the cyclone to overcome the combined effect of these negative factors for intensification. Remnant low status is now forecast in 72 hours, although it could occur sooner. The official forecast is lower relative to the previous one and near but a bit lower than a combination of the multi-model consensus, Decay-SHIPS, and LGEM. Center fixes suggest that the motion had been west-northwesterly throughout the day, and the initial motion estimate is left of the previous one or 305 degrees at 3 kt. The cyclone remains embedded in a weak steering environment between a low- to mid-level ridge to the east-northeast and a mid- to upper-level trough to the northwest. This synoptic pattern should allow for a generally slow northward or north-northeastward motion for the next few days before Amanda degenerates into a remnant low and turns westward or southwestward. Should Amanda weaken faster than forecast, little motion is expected, and its remnants could turn eastward in an anomalous low-level westerly flow. The official forecast is on the far western side of the guidance envelope, and is much slower than the previous forecast due primarily to the more southern initial position. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 14.6N 112.9W 60 KT 70 MPH 12H 28/1200Z 15.0N 112.8W 50 KT 60 MPH 24H 29/0000Z 15.8N 112.4W 40 KT 45 MPH 36H 29/1200Z 16.5N 111.9W 35 KT 40 MPH 48H 30/0000Z 17.0N 111.5W 30 KT 35 MPH 72H 31/0000Z 17.1N 111.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 01/0000Z 16.8N 111.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 02/0000Z 16.5N 111.8W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ Forecaster Kimberlain

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